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Topic:Hormones
Hormones in horses are chemical messengers produced by various glands and tissues, regulating numerous physiological processes essential for maintaining homeostasis. These hormones influence a wide range of functions, including growth, metabolism, reproduction, and stress responses. Key hormones in equine physiology include cortisol, estrogen, testosterone, and insulin, among others. The levels and effects of these hormones can vary based on factors such as age, sex, and environmental conditions, impacting overall health and performance. This page compiles peer-reviewed research studies and scholarly articles that explore the production, regulation, and physiological roles of hormones in equine biology.
Validation of nonradioactive chemiluminescent immunoassay methods for the analysis of thyroxine and cortisol in blood samples obtained from dogs, cats, and horses. The performances of a radioimmunoassay method, a chemiluminescent immunoassay method, and a chemiluminescent-enzyme immunoassay method were evaluated for the analysis of cortisol and total thyroxine in blood samples obtained from dogs, cats, horses, and humans (reference samples). The analysis of cortisol in human and animal samples exhibited good precision, linearity, and recovery. The 3 methods gave comparable values for the ACTH-induced increase and the dexamethasone-induced decrease in cortisol concentrations in animal samples. The recoveries of total thyroxine from human samples, analyzed...
Comparison of the effects of N-methyl-DL-aspartic acid on gonadotropin and prolactin secretion in anestrous mares and mares exhibiting estrous cycles during anestrus. This study investigated the hypothesis that for a subpopulation of horse mares continuation of estrous cycles during the nonbreeding season may be attributed to continued stimulatory glutamatergic activity on GnRH-secreting neurons. The gonadotropin response to the glutamatergic agonist N-methyl-DL-aspartic acid (NMA) was compared in cycling and anestrous mares during the nonbreeding season. It was anticipated that the gonadotropin response to NMA in cycling mares would be attenuated, compared with that of anestrous mares. The experiment used 16 anestrous mares and 15 mares that cycled during ...
Redox regulation of large conductance Ca(2+)-activated K+ channels in smooth muscle cells. The effects of sulfhydryl reduction/oxidation on the gating of large-conductance, Ca(2+)-activated K+ (maxi-K) channels were examined in excised patches from tracheal myocytes. Channel activity was modified by sulfhydryl redox agents applied to the cytosolic surface, but not the extracellular surface, of membrane patches. Sulfhydryl reducing agents dithiothreitol, beta-mercaptoethanol, and GSH augmented, whereas sulfhydryl oxidizing agents diamide, thimerosal, and 2,2'-dithiodipyridine inhibited, channel activity in a concentration-dependent manner. Channel stimulation by reduction and inhibit...
Characterization of prolactin- and growth hormone-binding proteins in milk and their diversity among species. The present study was undertaken to identify and characterize the diversity and species distribution of soluble prolactin binding-protein (PRL-BP) and growth hormone-binding protein (PRL-BP) in mammalian milk. We previously divided mammalian serum GH-BP into four main groups and identified a GH-BP with shared lactogenic/somatogenic properties in rabbit, horse, dog, pig and cat (Type III species). Here we describe PRL-BP in milk of Type III species and show it is relatively conserved within the group, having similar characteristics in terms of binding affinity for hGH (0.74-5.5 x 10(10) M(-1)),...
Biosynthesis and possible biological roles of progestagens during equine pregnancy and in the newborn foal. Major progress on the endocrinology of the pregnant mare has been possible thanks to the catheterised equine fetal preparation developed by Marian Silver. In particular, these preparations led to the identification of the source of progestagens within the feto-placental unit and provided the impetus for further work on their biosynthesis and biological activities. The biosynthesis of the progestagens involves close interaction between the fetus, the endometrium and the placenta, and gives rise to some fundamental biochemical questions. The biological role of the progestagens is also discussed:...
Effect of insulin-induced hypoglycaemia on secretion patterns and rates of corticotrophin-releasing hormone, arginine vasopressin and adrenocorticotrophin in horses. To study the effect of hypoglycaemia on secretion rates of corticotrophin-releasing hormone (CRH), arginine vasopressin (AVP) and ACTH in a non-ruminant species, a non-surgical method was used to collect pituitary venous (PitVen) blood every 0.5 or 1 min from seven horses before and after insulin administration (0.4 U/kg i.v.). To assess the effect of PitVen cannulation on results, peripheral hormones were also measured before and after insulin in five horses without PitVen cannulae. Insulin administration lowered plasma glucose in all horses (P < 0.0001; paired t-test). Cortisol concentrat...
Cloning, sequencing and in vitro functional expression of recombinant donkey follicle-stimulating hormone receptor: a new insight into the binding specificity of gonadotrophin receptors. Among all mammalian FSH receptors (FSH-R; including donkey (dk) FSH-R), only horse (hs) FSH-R does not bind hsLH/chorionic gonadotrophin (CG). In order to delineate the structural origin of hsFSH-R specificity precisely, we have cloned dkFSH-R cDNA from donkey testis mRNA by RT-PCR. Transiently expressed dkFSH-R endowed COS-7 cells with both hsLH/CG- and FSH-binding activity, as well as FSH-induced cAMP production. The deduced dkFSH-R amino acid sequence shares 96% identity with the hsFSH-R: notably, in the hormone-binding domain, the specificity of hsFSH-R may be ascribed to only four diverge...
Fetal calcium homeostasis. The mammalian fetus is maintained hypercalcaemic relative to its mother primarily by the action of a placental calcium pump located in the basal plasma membrane of the trophoblast. It is suggested that the activity of this pump is stimulated by a mid-molecular fragment of parathyroid hormone-related protein [PTHrP(38-94NH2)], produced in the placenta (and also in the parathyroid glands of fetal lambs and calves) as a result of post translational processing. In the sheep, calcitriol is an important determinant of fetal calcium homeostasis and it, too, stimulates the transport of calcium across ...
Cortisol concentrations in post competition horse urine: a French and British survey. The purpose of the present report was to estimate the population parameters of cortisol concentrations in urine, an endogenous hormone used as a 'doping' agent and for which an international threshold (1.0 micrograms/ml) has been proposed. Two data bases (French and UK) corresponding to 112 and 142 samples, respectively were considered. Urine was collected under specific post competition conditions. Cortisol concentrations were obtained by validated methods (HPLC for the French samples, and GC-MS for UK samples). No difference was observed between the 2 data sets and statistical analyses were ...
The relationship between the concentration of ionised calcium and parathyroid hormone-related protein (PTHrP[1-34]) in the milk of mares. Once lactation is established in mares, there is little change in the ionised calcium concentration in their milk. In contrast, the concentration of PTHrP(1-34) in the milk increases to a maximum level by the end of the second week of lactation, near which it remains for the rest of the lactation. As found in other species, the concentration of PTHrP(1-34) in mare's milk is considerably higher than that in plasma, sampled at the same time. No significant correlation could be demonstrated between the concentrations of PTHrP(1-34) and ionised calcium in the milk except during the last 10 weeks o...
Plasma glucose and cortisol responses to exogenous insulin in fasted donkeys. Susceptibility to equine hyperlipaemia is increased by poor food intake. To assess the contribution of changes in insulin sensitivity, plasma glucose and cortisol responses to an intravenous insulin challenge (0.4 IU kg-1 bodyweight) were compared with those observed after saline administration in six donkeys fasted either overnight or for three days. Three days of fasting decreased both the rate of insulin-induced hypoglycemia and the maximal hypoglycemic response. A transitory increase in plasma cortisol which peaked within one to four hours of insulin administration was observed in three of...
Acute effects of short-term feed deprivation and refeeding on circulating concentrations of metabolites, insulin-like growth factor I, insulin-like growth factor binding proteins, somatotropin, and thyroid hormones in adult geldings. Two studies were performed with Standardbred geldings 7 to 21 yr of age to determine the sequence of changes in blood plasma concentrations of some hormones and metabolites during feed deprivation for 48 h and for 12 h after refeeding. Plasma hormone and metabolite concentrations were determined with methods validated for horse plasma. Insulin-like growth factor binding proteins (IGFBP) were determined with radioligand analysis following SDS-PAGE electrophoresis. In both experiments, plasma concentrations of triiodothyronine and thyroxine decreased (P < .01) during feed deprivation and incr...
In-vitro modulation of plasminogen activator activity, prostaglandin E and nitric oxide production by interleukin-1 in pregnant mare serum gonadotrophin-primed theca-interstitial cells. To examine the participation of the theca-interstitial (TI) compartment in cytokine modulation of ovarian function, the effects of interleukin-1beta (IL-1) on plasminogen activator (PA) activity and on prostaglandin E (PGE) and nitric oxide (NO) production were examined in cultures of pregnant mare serum gonadotrophin (PMSG)-primed rat TI cells. Exposure to IL-1 (10 ng/ml) resulted in a 25% reduction (P < 0.001) in PA activity, concurrent with a 4.6-fold increase in the ability of the corresponding conditioned media to inhibit exogenous urokinase activity. IL-1 also produced a 4.7-fold incr...
Prolactin, gonadotropin, and hair shedding responses to daily sulpiride administration in geldings in winter. This experiment was designed to determine 1) the efficacy of daily s.c. injections of a dopamine antagonist, sulpiride, for increasing prolactin secretion in geldings in winter and 2) whether increasing prolactin concentrations would hasten the onset of hair shedding or enhance gonadotropin secretion. Five geldings each received vehicle (vegetable oil) or sulpiride (100 mg in vehicle) daily from February 8 through March 29. On February 8 and every 7 d thereafter through March 29, blood samples were drawn around treatment injections and hair samples were collected. On March 30, all geldings rec...
Prolactin administration to seasonally anestrous mares: reproductive, metabolic, and hair-shedding responses. Eight pony mares received 4 mg of recombinant porcine prolactin (rpPRL) daily for 45 d beginning on January 15; eight control mares received vehicle. Reproductive end points and various indicators of metabolism, hair shedding, and thyroid activity were monitored. Prolactin concentrations peaked in mares treated with rpPRL at 94 +/- 19 ng/mL 2 h after injection and were 5.1 +/- 1.7 ng/mL 24 h after injection. Treatment with rpPRL increased (P < .01) hair shedding within 14 d, which peaked at 28 d and then dropped precipitously. Binding of 125I-equine prolactin confirmed that antibodies were ...
Midazolam and ketamine induction before halothane anaesthesia in ponies: cardiorespiratory, endocrine and metabolic changes. Six Welsh gelding ponies were premedicated with 0.03 mg/kg of acepromazine intravenously (i.v.) prior to induction of anaesthesia with midazolam at 0.2 mg/kg and ketamine at 2 mg/kg i.v.. Anaesthesia was maintained for 2 h using 1.2% halothane concentration in oxygen. Heart rate, electrocardiograph (ECG), arterial blood pressure, respiratory rate, blood gases, temperature, haematocrit, plasma arginine vasopressin (AVP), dynorphin, beta-endorphin, adrenocorticotropic hormone (ACTH), cortisol, dopamine, noradrenaline, adrenaline, glucose and lactate concentrations were measured before and after ...
Use of the GnRH analogue, deslorelin acetate, in a slow-release implant to accelerate ovulation in oestrous mares. In two separate controlled clinical trials, the efficacy and safety of 2.2 mg of the GnRH analogue deslorelin, administered subcutaneously as a short-term implant to normally cycling mares in oestrus with a dominant ovarian follicle more than 30 mm in diameter, were evaluated, using a placebo as a negative control. The oestrous cycle of each mare was followed by teasing, palpation per rectum and transrectal ultrasonography. Follicles were monitored every 24 hours by ultrasonography until ovulation occurred. The mares were either mated naturally or inseminated artificially. In trial 1, 174 mare...
Body weight, fluid, electrolyte, and hormonal changes in horses competing in 50- and 100-mile endurance rides. To investigate effects of prolonged exercise on fluid and electrolyte losses in horses competing in 50- and 100-mile endurance competitions, with emphasis on recovery. Methods: Changes in body weight (BW); PCV; serum osmolality; plasma total protein, lactate, aldosterone, and serum electrolyte concentrations; and exchangeable cation content were measured in 12 and 7 horses before and after and before, during, and after successful completion of 50- and 100-mile endurance rides, respectively. Methods: BW was measured by use of a portable load bar scale, and blood samples were collected during th...
Expression of horse and donkey LH in COS-7 cells: evidence for low FSH activity in donkey LH compared with horse LH. Horse (Equus caballus) luteinizing hormone (eLH) and chorionic gonadotrophin (eCG), which have the same amino acid sequence, are unusual in that, although they express only LH activity in equids, they express dual LH and FSH activities in all other species tested. Donkey (Equus asinus) LH (dkLH) and CG (dkCG), which also share an identical peptide backbone, have been less well characterized and conflicting results concerning their FSH activity in heterologous species have appeared in the literature. In order to assess and compare the intrinsic LH and FSH activities of the horse and donkey LHs ...
Patterns of secretion of GnRH, LH and FSH during the postovulatory period in mares: mechanisms prolonging the LH surge. To study the mechanisms responsible for the unusually slow decline of the ovulatory LH surge in mares, secretion patterns of GnRH, LH and FSH were monitored in pituitary venous blood collected every 2 or 5 min for 10.5-18.0 h from five mares on the third (n = 4) or fifth day after ovulation (first sampling period). To determine the effectiveness of progesterone negative feedback, mares were then given a luteolytic dose of a prostaglandin analogue (PGF2 alpha) and pituitary venous sampling (every 2 or 5 min for 16 h) recommenced 20-22 h later (second sampling period). During the declining arm o...
Effect of feeding and feed deprivation on plasma concentrations of prolactin, insulin, growth hormone, and metabolites in horses. Two experiments were conducted to determine 1) the prolactin response to different kinds of feedstuffs in stallions and 2) the effects of total feed deprivation on prolactin secretion in mares and its interaction with the prolactin response to feeding. Experiment 1 was performed with stallions as a 6 x 6 Latin square: A) no feed; B) pelleted feed fed to meet 82.5% of the horses' CP requirements; C) pelleted feed at 25% of the amount in B; D) pelleted feed as in B plus water ad libitum; E) cracked corn at the weight in B; and F) chopped alfalfa at the weight in B. The positive prolactin respons...
A developmental switch in expression from blastocyst to endometrial/placental-type cytochrome P450 aromatase genes in the pig and horse. Pig blastocysts exhibit a transient period of estrogen production at periimplantation, with a second, more sustained period of estrogen synthesis occurring in endometrium and placenta at later pregnancy. Previously we reported the isolation of cDNA clones encoding a novel isoform of cytochrome P450 aromatase (the terminal enzyme in the estrogen biosynthetic pathway) from porcine periimplantation blastocysts. The present study investigated pregnancy-associated expression, in blastocysts and maternal reproductive tract tissues of this and an additional mRNA transcript encoding a distinct P450 ar...
Serum thyroid hormone concentrations in New Zealand horses. Total thyroxine and total tri-iodothyronine concentrations were measured in the sera from 125 horses of mixed age, breed and sex, and varied clinical histories. While low serum thyroxine concentrations were detected in 35 horses, the majority of those horses had serum thyroxine values within the reference range when retested. Only one horse had a mildly decreased serum tri-iodothyronine concentration. Those horses in which the serum thyroxine concentration was low when retested had a normal thyrotropin releasing hormone stimulation test. Hypothyroidism was not diagnosed in any horses in this s...
The influence of progesterone-induced proteins on glucose metabolism in early equine embryos. The influence of different maternal plasma progesterone concentrations on embryonic glucose metabolism was studied. Uterine flushes were obtained after treating ovariectomized mares (n = 3) with 0 (control), 100 or 200 mg progesterone daily for 7 d. A group of progesterone-induced proteins (PIP) of Mr approximately 20,000 were identified in flushes from progesterone treatments by SDS-PAGE but were not observed in control flushes. Progesterone-induced proteins were removed from half the pooled flush in each treatment group by Sepharose blue CL-6B. In a 3 x 2 factorial (progesterone treatments, ...
Production of free estrogens and estrogen conjugates by the preimplantation equine embryo. In vitro production of free estrogens and estrogen conjugates by intact Day 12.5, 13.5 and 14.5 equine embryos was measured at 2-h intervals over a 24-h culture period. Production of free estrogens was higher for Day 14.5 than Day 12.5 embryos. Differences in production of conjugated estrogens were not significant, but a trend toward increased production with increased age of embryo was apparent. No trend toward increased free and conjugated estrogen production per cell was observed with age. Embryo diameter and number of cells increased with age but varied considerably within groups. The amou...
