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Topic:Pituitary
The pituitary gland in horses is a small, yet significant endocrine organ located at the base of the brain. It is responsible for producing and releasing hormones that regulate various physiological processes, including growth, metabolism, and reproduction. The gland is divided into two main parts: the anterior pituitary, which secretes hormones such as adrenocorticotropic hormone (ACTH) and growth hormone (GH), and the posterior pituitary, which releases hormones like vasopressin and oxytocin. Changes or dysfunctions in pituitary function can lead to conditions such as pituitary pars intermedia dysfunction (PPID), commonly known as equine Cushing's disease, which affects older horses. This page compiles peer-reviewed research studies and scholarly articles that explore the structure, function, and clinical implications of the pituitary gland in equine health.
Direct effects of free and conjugated steroids on GnRH stimulated LH release in cultured equine anterior pituitary cells. Enzymatically dispersed anterior pituitary cells from donor mares were cultured for 48 h in alpha-modified Eagles' medium containing 10% steroid-free horse serum. The cells were then incubated for 24 h in fresh medium oestrogen followed by a 4-h incubation with or without GnRH. Media and cell extracts were analyzed for LH by radioimmunoassay. In the first series of experiments, pituitary cells from Day-3 dioestrous mares were preincubated with ethanol (control) or different concentrations of E2 (10(-11) to 10(-7) M) for 24 h prior to a 4-h incubation without (basal) or with 1.0 nM GnRH. E2 inc...
Ovarian response in mares to prolonged treatment with exogenous equine pituitary gonadotrophins. Twelve anoestrous mares were treated with an intravaginal sponge containing 0.5 g allyl trembolone (Regumate; Roussel UCLAF, Paris) and 50 mg oestradiol benzoate for 7 days, followed by daily intramuscular (i.m.) injections of 25 mg crude equine pituitary extract (CEG), with (n = 6) or without (n = 6) 0.25 mg porcine growth hormone (pGH). No difference in ovarian response to this superovulation treatment was observed between the 2 groups (2.2 +/- 0.4 vs 2.3 +/- 0.4 ovulations per mare, respectively). CEG treatment was then combined with allyl trembolone (40 mg per os per day) and prolonged in ...
Prolonged pulsatile administration of gonadotrophin-releasing hormone (GnRH) to fertile stallions. Hormonal effects of prolonged administration of gonadotrophin-releasing hormone (GnRH) were investigated in 7 fertile stallions in winter and summer. The stallions were divided into 4 groups so that 1 animal received 0.625 micrograms of GnRH and each of 2 animals received 1.25, 2.5 or 5.0 micrograms of GnRH subcutaneously every 30 min for 5 days. Daily blood samples were collected from 5 days before to 5 days after treatment for measurement of plasma concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone (T) and oestrogen conjugates (EC). Five-minute blood...
Partial purification and characterization of rhinoceros gonadotropins, growth hormone, and prolactin: comparison with the horse and sheep. The rhinoceros is an endangered species related to the horse family. Little is known of its reproductive endocrinology. The objectives of this study were to partially purify rhinoceros pituitary hormones, determine which assays could be used for their assessment, and to ascertain whether rhinoceros LH possesses the intrinsic FSH activity of equine LH. A single pituitary each from a White (1.3 g) and a Black (1.2 g) Rhinoceros was homogenized and extracted (pH 9.5), then subjected to pH and salt fractionation, and ion-exchange chromatography (DEAE and Sephadex SP-C50) to yield partially purifie...
Changes in luteinizing hormone bioactivity associated with gonadotrophin pulses in the cycling mare. Equine plasma luteinizing hormone (LH) possesses both biological (in vitro bioassay, B) and immunological (radioimmunoassay, I) activities and the ratio of B:I varies with stage of the oestrous cycle. To estimate the contribution made by pituitary secretion and peripheral metabolism to changes in the B:I ratio, pituitary venous effluent and circulating plasma from 5 dioestrous and 2 oestrous mares were analyzed using both an in vitro bioassay and a radioimmunoassay. During dioestrus, LH was released in a pulsatile fashion with a frequency of 1.4 pulses/24 h and a pulse duration of 20-40 min (c...
Immunocytochemical demonstration of proopiomelanocortin-derived peptides in pituitary adenomas of the pars intermedia in horses. Adenomas of the pars intermedia from 19 horses and normal pituitary glands from seven horses were evaluated histologically and immunocytochemically for adrenocorticotropic hormone (ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH), beta-endorphin (beta-END), proopiomelanocortin (POMC), prolactin, neuron specific enolase, and glial fibrillary acidic protein (GFAP). The 26 horses ranged in age from 7 to 31 years. Histologically, all adenomas had a uniform pattern characterized by cords of large columnar cells forming palisades and pseudoacini separated by a delicate fibrovascular stroma. I...
Different combinations of regulatory elements may account for expression of the glycoprotein hormone alpha-subunit gene in primate and horse placenta. Expression of the glycoprotein hormone alpha-subunit gene occurs in the pituitaries of all mammals and in the placentas of primates and horses. In humans, tandem cAMP response elements (CREs), located in the proximal promoter-regulatory region of the alpha-subunit gene, act together with an adjacent upstream regulatory element to confer placenta-specific expression. Here, we report that the alpha-subunit genes of Old World Monkeys contain a single functional CRE. This suggests that tandem CREs are unique to higher primates and humans and are not absolutely required for placenta-specific expres...
Effects of active immunization against GnRH on LH, FSH and prolactin storage, secretion and response to their secretagogues in pony geldings. Six pony geldings were actively immunized against GnRH conjugated to bovine serum albumin (BSA) to study 1) the relative dependency of LH and FSH storage, secretion and response to GnRH analog on GnRH bioavailability and 2) the effects of reduced GnRH bioavailability on GnRH storage in the hypothalamus. Five geldings were immunized against BSA. Geldings were immunized in December and 4, 8, 14, 20, 26 and 32 wk later. Ponies immunized against GnRH had increased (P less than .01) GnRH binding in plasma within 6 wk. By June, plasma concentrations of LH and FSH in ponies immunized against GnRH had...
The influence of photoperiod on gonadotrophin-releasing hormone stimulated luteinising hormone release in the anoestrous mare. The transition from anoestrus to oestrus in mares is controlled by photoperiod. The present study examined whether additional daylength would accelerate the mares' response to gonadotrophin-releasing-hormone (GnRH). Nine anoestrous mares were placed under ambient or artificial long lighting on 7th January. The four month experimental period was divided into a three-day sequence which was repeated at 21 day intervals. Ovaries were palpated rectally on Day 1; saline was injected (1 ml intravenously [iv]) on Day 2; GnRH was administered (0.59 microgram/kg bodyweight iv) on Day 3. Blood was taken ...
Effect of maternal treatment with altrenogest on pituitary response to exogenous GnRH in pubertal stallions. The pituitary response to exogenous GnRH was studied in 8 colts of Quarter Horse phenotype from 32 to 96 weeks of age. Colts were from dams treated daily from Day 20 to 325 of gestation with (1) 2 ml neobee oil per 50 kg body weight (controls); or (2) 2 ml altrenogest per 50 kg body weight. GnRH challenges (5 micrograms/kg body weight) were administered every 8 weeks from 32 to 96 weeks of age to estimate pituitary content of LH. Blood samples were collected every 20 min for 4 h before GnRH and 15, 30, 45, 60, 90, 120, 180, 240 and 360 min after GnRH. Serum concentrations of LH and FSH were de...
Effect of maternal treatment with altrenogest on age at puberty, hormone concentrations, pituitary response to exogenous GnRH, oestrous cycle characteristics and fertility of fillies. Puberty was studied using 15 fillies of Quarter Horse phenotype. Fillies were from dams treated daily from Days 20 to 325 of gestation with: (1) 2 ml neobee oil per 50 kg body weight (controls); or (2) 2 ml altrenogest (2.2 mg/ml) per 50 kg body weight. The clitoris was measured at birth and approximately every 12 weeks until 84 weeks of age. Blood samples were collected from 9 fillies (5 treated, 4 controls) every 4 days over a 28-day period at 8-week intervals from 4 to 68 weeks of age; sampling continued every 4 days after 72 weeks of age until first oestrus. Blood samples were collected da...
Hypertrophic osteopathy in a pony with a pituitary adenoma. Hypertrophic osteopathy was diagnosed in a pony that had no antemortem or postmortem evidence of an intrathoracic lesion. With a history of hirsutism in an aged pony, a pituitary adenoma was suspected, and evaluation of plasma cortisol and insulin values and their response to thyrotropin-releasing hormone supported the diagnosis.
Effect of an osmotic stimulus on the secretion of arginine vasopressin and adrenocorticotropin in the horse. Arginine vasopressin (AVP) is released in response to changes in blood osmolality and is also a putative secretagogue for ACTH. However, it is unclear whether osmotically generated increases in AVP in the physiological range influence ACTH secretion. We have studied this question using our unique noninvasive technique for collecting pituitary venous blood in six normal conscious horses that received an iv infusion of hypertonic saline (HS; 5%, 0.07 ml/kg.min) for 45-60 min. Pituitary and jugular venous samples were collected every 5 min for 40 min before, during, and for 20 min after HS. Durin...
Changes in serum concentrations of luteinizing hormone and follicle-stimulating hormone following injection of gonadotropin-releasing hormone during pregnancy and after parturition in mares. High concentrations of estrogens in the peripheral circulation during late gestation inhibit synthesis of LH and markedly reduce pituitary content of LH at the end of pregnancy in most domestic species. Because blood concentrations of estrogen peak shortly before mid-gestation in the mare and then gradually decrease until parturition, we hypothesized that pituitary content of LH may increase during late gestation. To test this hypothesis 10 horse mares were challenged with a maximally stimulatory dose (2 micrograms/kg) of GnRH on d 240 and 320 of gestation and d 3 after parturition. A separate...
Influences of season and artificial photoperiod on stallions: pituitary and testicular responses to exogenous GnRH. Effects of season and photoperiod on the anterior pituitary gland and testes were studied by responses to exogenous GnRH. Stallions were assigned to one of three treatments: 1) control, exposed to natural day length; 2) S-L, 8 h of light and 16 h dark (8:16) for 20 wk beginning July 16, 1982 then 16:8 from December 2, 1982 until March 5, 1984; or 3) S-S, 8:16 from July 16, 1982 until March 5, 1984. Approximately every 8 wk, stallions were administered GnRH (2 micrograms/kg BW) and blood was sampled at 20-min intervals for 2 h before and 8 h after GnRH administration. Concentrations of LH, FSH ...
The effects of cortisol, vasopressin (AVP), and corticotropin-releasing factor administration on pulsatile adrenocorticotropin, alpha-melanocyte-stimulating hormone, and AVP secretion in the pituitary venous effluent of the horse. Plasma ACTH, arginine vasopressin (AVP), and alpha MSH were measured in pituitary venous effluent at 5-min intervals from five unanesthetized horses during cortisol infusion and after an iv bolus of AVP or ovine (o) CRF. In control experiments (no hormone) there was a significant overall correlation between the timing of concentration changes in ACTH and alpha MSH. Cortisol infusion increased jugular cortisol levels by 70% and was associated with a reduction in mean ACTH, AVP, and alpha MSH secretion rates and ACTH peak secretion rate, but did not alter the observed pulse frequencies of these ...
Differences in diagnostic test results and hematologic data between aged and young horses. Hematologic data and results of diagnostic tests were compared between aged (greater than or equal to 20 years old) and young (less than or equal to 5 years old) horses to identify hematologic and metabolic changes associated with aging. Initial data were obtained from 8 aged and 6 young mares (group 1). Similar data were collected from a second group of aged (3 mares and 3 geldings) and young (1 mare and 5 geldings) horses (group 2). Dexamethasone suppression tests (DST) and necropsies were performed on 6 additional mares and mare 8 from group 1 (group 3). Complete blood counts and serum bioc...
Primary structure of equine pituitary prolactin. Equine prolactin was determined to be a single chain protein of 199 amino acid containing two tryptophan and six cysteine residues, as found in other mammalian prolactins. The primary sequence of equine prolactin was obtained by automated Edman analyses of S-carboxymethylated protein and proteolytic fragments of modified protein. Of the known prolactin sequences, equine prolactin shows closest homology with porcine (93%) and fin whale (87-91%) prolactins. Genetic mutations have produced changes in 17 of 199 residues of equine prolactin relative to its putative ancestral precursor. Since equine...
Secretion rates and short-term patterns of gonadotrophin-releasing hormone, FSH and LH in the normal stallion in the breeding season. Pituitary venous blood was collected by a painless nonsurgical cannulation method from five ambulatory stallions at 5-min intervals for 5-6 h during the breeding season. In four adult stallions, statistical analysis showed that pulses of gonadotrophin-releasing hormone (GnRH) and LH were coincident (P less than 0.01), as were pulses of FSH and LH (P less than 0.05). Furthermore, the patterns of changes in concentration of FSH and LH were highly correlated in each of the four stallions. However, seemingly ineffective pulses of GnRH were also observed, with 28% of GnRH pulses failing to induce a...
Conformational restrictions of the sheep testicular receptor discriminates pituitary lutropin and placental gonadotropins. A membrane preparation from the testis of maturing Dorset-Leicester-Suffolk sheep, capable of discriminating pituitary LH (lutropin) from placental gonadotropins human choriogonadotropin (hCG) and equine choriogonadotropin is described. Maximum binding of 125I-oLH (ovine lutropin) to the testicular receptors occurred at 4 degrees C in a rapid manner, attaining equilibrium in 12-16 h. Under such optimal conditions, only unlabeled ovine LH or the structurally identical bovine LH effectively competed for receptor occupation. Other highly purified pituitary LH preparations from rat and human pitui...
Effect of isolation stress on concentrations of arginine vasopressin, alpha-melanocyte-stimulating hormone and ACTH in the pituitary venous effluent of the normal horse. A non-surgical, non-stressful technique was used for collection of pituitary venous blood from five conscious horses every minute for two 10-min periods before and during isolation from the herd, which caused a predictable, yet humane and physiological, emotional stress. Pituitary blood was also sampled every 5 min for two approximately 90-min periods before and after isolation, while jugular blood was sampled every 15 min throughout the experiment. During isolation, all horses became agitated, hyperventilating and sweating. Packed red cell volume increased, as did pituitary venous concentrati...
Adrenocorticotropin-containing neoplastic cells in a pars intermedia adenoma in a horse. Pituitary-dependent hyperadrenocorticism was diagnosed in a 14-year-old Arabian mare with chronic weight loss, hirsutism, polyuria, and polydipsia. The mare had a stress leukogram, glucosuria, and consistent hyperglycemia. Plasma glucose concentrations were resistant to suppression by insulin. Plasma cortisol concentrations were within normal limits, but did not respond to dexamethasone suppression and had an exaggerated response to ACTH stimulation. At necropsy, a chromophobe adenoma of the pars intermedia of the pituitary gland was found. The zona fasciculata of the adrenal cortex and the pa...
Evaluation of thyroid, adrenal, and pituitary function. The clinical signs and endocrinologic abnormalities that characterize horses with pituitary, thyroid, and adrenal dysfunction are described. Laboratory tests and hormonal assays useful for evaluating horses with suspected endocrinopathies are discussed.
Nucleotide (cDNA) sequence encoding the horse gonadotrophin alpha-subunit. Several cDNA clones corresponding to mRNA for the alpha-subunit of the horse (Equus caballus) pituitary and placental (chorionic) gonadotrophic hormones have been isolated and sequenced. Polyadenylated mRNA was purified from horse pituitary glands (the source of FSH and LH) and horse placental tissues (the source of chorionic gonadotrophin; CG). The mRNA preparations were characterized by in-vitro translation and Northern hybridization techniques using human and ovine gonadotrophin cDNA clones as probes. Complementary DNA libraries were created from the pituitary and placental mRNAs and a huma...
Effects of physiologic and pharmacologic agents on serum prolactin concentrations in the nonpregnant mare. Four studies were conducted to evaluate the effects of several physiologic and pharmacologic agents on serum prolactin concentrations in the nonpregnant mare. An increase in prolactin measured in response to administration of thyrotropin-releasing hormone (TRH; 50 micrograms, iv) was found not to vary (P = .20) in mares in estrus compared with mares in diestrus (5 to 10 d post-ovulation). Administration in the dopamine receptor blocker, metoclopramide (25 or 100 mg, im), rapidly increased serum prolactin, and the response was dependent on dose administered (total prolactin measured for 420 min...
Secretion rates and short-term patterns of gonadotrophin-releasing hormone, FSH and LH throughout the periovulatory period in the mare. We have developed a non-surgical technique for long-term collection of pituitary venous blood which consists of slightly diluted hypophysial portal blood into which pituitary hormones have been secreted. In these experiments jugular and pituitary venous blood samples were collected from five unmedicated, ambulatory mares at 5-min intervals for 2-6 h on 11 occasions during the 6 days surrounding the ovulatory LH peak. Jugular blood only was collected from another five periovulatory mares without pituitary cannulae. The duration of oestrus was similar in mares with and without pituitary cannulae...
Structural studies on equine glycoprotein hormones. Amino acid sequence of equine chorionic gonadotropin beta-subunit. The complete amino acid sequence of the beta-subunit of equine chorionic gonadotropin (eCG beta) has been established by both automated Edman and manual 5-dimethylaminonaphthalene-1-sulfonyl-Edman degradations. Specific fragments were produced by cleavage with Staphylococcus aureus V8 protease, trypsin, or dilute HCl. For the sequence analyses of the heavily glycosylated COOH-terminal portion, a chemical deglycosylation procedure with trifluoromethanesulfonic acid was employed. The peptide chain of eCG beta consists of 149 amino acid residues. Five or more oligosaccharide chains are attached t...
Biological and immunological properties of zebra pituitary gonadotropins: comparison with horse and donkey gonadotropins. Previous studies from this laboratory have described the properties of purified luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from horse and donkey anterior pituitary glands. The present study afforded the opportunity to further characterize these previously purified hormone preparations and to compare them with enriched gonadotropin fractions from zebra pituitary glands. Although a single LH and FSH fraction was usually obtained for each pool of pituitaries, two separate zebra LH and two donkey FSH preparations were generated. Purified hormone preparations from the horse wer...
Pituitary responsiveness of mares challenged with GnRH at various stages of the transition into the breeding season. Four groups of mares, representing anestrus (AN; n = 8), early transition (ET; n = 7), late transition (LT; n = 8) and estrus (EST; n = 12) were used to examine release of luteinizing hormone (LH) and follicle stimulating hormone (FSH) after a bolus injection of gonadotropin releasing hormone (GnRH) during the transition from anestrus into the breeding season. Estrous mares received GnRH on d 2 or 3 of estrus in the cycle immediately preceding slaughter. Anestrous, ET and LT mares received GnRH exactly 1 wk prior to slaughter. A single injection of GnRH (Sigma LHRH, L-0507, 2.0 micrograms/kg b...
