Effects of short-term stress, xylazine tranquilization and anesthetization with xylazine plus ketamine on plasma concentrations of cortisol, luteinizing hormone, follicle stimulating hormone and prolactin in ovariectomized pony mares

Long-term ovariectomized pony mares were subjected to one of four treatments: 1) control group - no treatment, 2) stressed group - 5 min of restraint via a twitch, 3) tranquilized group - administered xylazine (1.1 mg i.v. per kg of body weight), and 4) anesthetized group - administered xylazine followed 2 min later by ketamine (2.2 mg i.v. per kg of body weight). Blood samples were taken at -40, -30, -20, -10, -0.5, 10, 20, 30, 40, 50, 60 and 90 min and at 2, 3, 4, 6, 8 and 24 h relative to onset of treatment. Stress increased (P<0.05) cortisol concentrations 20 to 50 min after treatment and again at 6 and 8 h. Tranquilization had no effect on cortisol concentrations, whereas anesthetization increased (P<0.05) cortisol concentrations from 90 min through 8 h after treatment. Concentrations of luteinizing hormone (LH) and follicle stimulating hormone (FSH) did not vary (P>0.1) relative to pretreatment in any group of mares. Concentrations of prolactin were 2.7-fold higher (P<0.05) 24 h after treatment in all four groups, indicating some procedural or environmental influence on prolactin secretion. There was a transient increase (P<0.06) in prolactin concentrations in anesthetized mares 30 min after treatment. Although two of these three commonly used methods of restraint did affect cortisol concentrations, there was no effect on plasma concentrations of LH or FSH. Thus, we conclude that such methods of restraint can be used in short-term situations without disturbing estimates of LH and FSH secretion. However, when prolactin concentrations are to be measured, anesthesia with ketamine should not be used.     

The effects of different anaesthetic treatments on the adreno-cortical functions and glucose levels in NZW rabbits

The effects of five anaesthetics on the corticosterone, cortisol and glucose concentrations were investigated in the NZW rabbit. Sixty animals were assigned to 6 treatment groups (n= 10 per group): control ( iv saline solution injection), ketamine (10 mg/kg iv) with either xylazine (3 mg/kg iv) or diazepam (2 mg/kg iv), pentobarbitone (30 mg/kg iv), thiopentone (20 mg/kg iv) and fentanyl/droperidol (1 mg/kg sc). Plasma glucocorticoids were measured by competitive enzymeimmunoassay EIA and glucose by an autoanalyzer, previously validated for this species in both cases. Blood samples were obtained at 6 time-points: before injection, at 10, 30, 60, 120 min and 24 h after injection of the anaesthetics/saline. A significant decrease of plasma glucocorticoids at 10-60 min was observed in the pentobarbitone and fentanyl/ droperidol groups, whereas the administration of ketamine/diazepam or thiopentone stimulated plasma glucocorticoid release, principally in the recovery period. However, in the ketamine/xylazine group no changes were observed in the glucocorticoid levels, except for a significative increase of cortisol at 60-120 min. Glucose levels significantly increased after ketamine/diazepam administration and principally, after ketamine/xylazine treatment. The present data suggest that ketamine/xylazine has little effect on glucocorticoid levels and provides an adequate level of surgical anaesthesia, hence it would be the anaesthetic of choice, although the hyperglycaemic effect after injection has to be considered for any experimental procedures in rabbits.     

The effects of serotonergic and adrenergic receptor antagonist on prolactin release in the monkey.

The influence of serotonergic and adrenergic antagonists on serum prolactin levels was studied in ketamine anesthetized monkeys. Methysergide, a serotonergic receptor blocker, at 0.035, 0.1 and 1 mg/kg body weight induced a rapid and transient increase in serum prolactin. Cyproheptadine, another serotonergic receptor blocker, at 0.05, 0.5 and 1 mg/kg induced a rapid and sustained increase in serum prolactin. SQ 10631, a third serotonergic receptor blocker, had a minimal effect on increasing basal prolactin levels even at doses as high as 10 mg/kg. Propranolol, a β adrenergic blocker, at a dose of 5 mg/kg induced a small sustained increase in serum prolactin, while a lower dose (1 mg/kg) had a slight but significant effect. Phentolamine, an α adrenergic receptor blocker, at a dose of 5 mg/kg induced a rapid and transient increase in plasma prolactin while a lower dose (1 mg/kg) had no effect. Phenoxybenzamine, a potent α adrenergic receptor blocker, had only a minimal effect on prolactin release even at doses of 3 and 5 mg/kg. It appears that the time course and extent of prolactin release differs among neural antagonists even within the same biogenic amine system.     

Exercise training and the differential prolactin response in male and female rats

Adult male and female Sprague-Dawley rats were trained on a horizontal treadmill for 0, 1, 3, 5, or 7 days/wk for 10 wk. Speed and duration were progressively increased over 5 wk to a maximum of 20 m/min for 1 h. Between weeks 9 and 10 of training, animals were placed on the nonmoving treadmill, and blood (500 microliters) was sampled via chronic venous cannulas 30 min before, 0, 10, 20, 30, 45, and 60 min during exercise, and 15, 30, 60, 90, and 120 min after exercise. In another study, resting animals in the various groups were injected with thyrotropin-releasing hormone (TRH; 2 micrograms/kg for males and 0.4 microgram/kg for females) to determine pituitary prolactin responsiveness. In males, exercise induced a significant increase in plasma prolactin levels, with the greatest increase observed in the least trained and the smallest increase in the most highly trained animals. Female rats displayed the opposite trend with the greatest increase in prolactin secretion observed in the highest trained and the smallest increase observed in the least trained animals. TRH induced similar increases in plasma prolactin in all male groups, whereas TRH-induced prolactin release was greatest in the highest trained and smallest in the least trained females. The reduced prolactin response in highly trained males may reflect their acclimation to repetitive exercise stress, whereas the enhanced response in the highly trained female rats appears to result from increased pituitary sensitivity to prolactin-releasing factors.     

Effect of nasal instillation of female urine or vaginal exudate on serum cortisol and prolactin levels in isolated and anesthetized male rhesus monkeys (Macaca mulatta)

Two male adult rhesus monkeys were used and caged individually. The room was temperature-controlled having a light-dark period of 12/12 hours. The animals were rapidly immobilized and immediately anesthetized with ketamine i. m. (10 mg/kg of body weight). They were bled four times at 15, 30, 45 and 60 mins after the ketamine injection, twice a week for 6 weeks. When necessary, maintenance doses of ketamine were administered. The serum levels of cortisol and prolactin after nasal instillation of a suspension of vaginal exudate showed lower values than in control conditions (nasal instillation of saline). The control levels of cortisol tended to increase up to 60 mins, whilst in experimental conditions (nasal instillation of female urine or vaginal exudate) did not show such an increase. Cortisol remained similar during the sampling and similar to the 15 mins control levels, but the difference is statistically significant only after instillation of vaginal exudate as compared with control. The levels of prolactin did not show significant variations during sampling either in control or after female urine instillation. However, the instillation of vaginal exudate decreased the prolactin levels at 15 mins which tended to recover the control levels up to 60 mins. These results support the hypothesis, discussed in a previous paper, that some chemical information from females suppresses or mitigates the effect of acute stress resulting from handling the animals before anesthesia.     

Prostaglandin F2alpha (PGF2alpha) and prolactin secretion in rats.

Plasma prolactin and F-prostaglandins (PGF) were measured anesthetized male Sprague-Dawley rats before and at 15, 30, 45 and 60 minutes following i.v. injection of either PGF2alpha (4 mg/kg), chlorpromazine, 1 mg/kg or chlorpormazine (1 mg/kg) after pretreatment with i.p. indomethacin (2 mg/kg). Following PGF2alpha administration, plasma prolactin levels increased significantly only at 15 and 30 minutes in spite of extremely high PGF levels throughout 60 minutes. Besides the expected rise in plasma prolactin, chlorpromazine caused a transient but statistically significant increase in PGF. Indomethacin blocked the chlorpormazine-induced PGF rise but not prolactin increase. Animals stressed with ether anesthesia showed elevation of plasma prolactin, which was not blocked by indomethacin although PGF concentration fell. Theese results indicate that PGF2alpha can stimulate prolactin release. This effect does not appear to be physiologic since very high PGF levels are required. Furthermore, blockade of prostaglandin synthesis by indomethacin does not prevent the release of prolactin in response to chlorpormazine or stress. Our findings do not support a possible role of PGFs as intermediaries in prolactin release. However, it is possible that PGFs may work through other mechanisms not investigated in our study.     

Clinical, biological and hormonal study of mid-pregnancy termination in cats with aglepristone

In order to evaluate the efficacy, the safety and the variation in plasma concentrations of estrogens, progesterone, PGFM, oxytocin, cortisol and prolactin after mid-pregnancy termination induced by aglepristone, 61 pregnant queens (33.3 + 4.2 days), were injected subcutaneously with 15 [corrected] mg/kg aglepristone, (Alizine) [corrected] repeated once 24 h later. Five queens served as control and received a placebo. The efficacy of aglepristone was 88.5% and termination of pregnancy was achieved in 50% of the queens within 3 days. Brief periods of depression and anorexia were noted in 9.3% of the queens before fetal expulsion (these symptoms were attributed to the phenomenon of fetal expulsions). Not one of the queens that aborted developed uterine disease. There were no changes in plasma concentrations of estrogen, prostaglandin, prolactin or oxytocin following aglepristone administration. However, there were significant increases in plasma concentrations of progesterone and cortisol 60 and 30 h, respectively, after aglepristone administration. Termination of pregnancy occurred with high plasma progesterone concentrations. Fetal expulsion was characterised by an increase in estrogen, PGFM and oxytocin concentrations, whereas prolactin and cortisol levels remained at a basal level.     

Influence of pimozide on a TRH induced TSH secretion in the rat during food deprivation.

Adult Wistar rats food deprived for 3 days had lower basal levels of TSH compared to normal fed animals. An increase of these lower levels to normal values was obtained following a prolonged (injections during 3 consecutive days) or acute treatment (single injection) with pimozide (1 mg/injection). Blood samples obtained after the last or an only injection of pimozide contained profound increased prolactin levels. Prolactin increase was more than 100-fold in fed and more than 30-fold in starved rats following prolonged pimozide treatment and more than 25-fold and 10-fold following a single injection of pimozide. An injection of 250 ng of TRH increased plasma concentrations of TSH in all groups, but this increase was more pronounced in fasted rats injected with pimozide during 3 consecutive days. It is concluded that fasting results in a dopaminergic inhibition of the sensitivity of the thyrotrophs to a TRH challenge.     

Hyperprolactinemia associated with chronic renal failure in the rat

Patients with CRF exhibit hyperprolactinemia and resistance to the prolactin-suppressive effects of dopamine. In order to explore the pathogenetic mechanisms involved, an animal model of CRF was developed in the adult male rat bearing an indwelling right atrial catheter by performing a two stage 5/6 nephrectomy (NX). Following NX, serum creatinine levels rose to a value of 1.36 +/- 0.2 mg/dl at 8 weeks as compared to sham-operated controls (0.31 +/- 0.1, P less than 0.01). There was a parallel increase in plasma prolactin levels in NX animals with values significantly greater than in controls by 8 weeks (49 +/- 11 vs 17 +/- 2 ng/ml, P less than 0.02). At 8 weeks, the plasma prolactin responses to metoclopramide (500 micrograms/kg, iv) were similar in unanesthetized NX and sham-operated control animals. The prolactin-suppressive effects of an iv dopamine infusion (6 micrograms/kg/min X 30 min) was also similar in the two groups (46 +/- 8% vs 40 +/- 10% suppression). The responses of lactotrophs in vitro were compared in NX and control animals at 8 weeks. Basal prolactin release during 4 h was similar in the two groups as were the suppressive responses to dopamine and bromocriptine. The results indicate that the rat with CRF, like human develops hyperprolactinemia. In contrast to the human, however, responses to dopaminergic agonists and antagonists in vivo and in vitro are unimpaired, indicating that hyperprolactinemia in rats with CRF occurs on a non-dopaminergic basis.     

Pituitary cyclic AMP and plasma hormone responses to epinephrine administration in vivo

The present study was conducted to characterize the in vivo effects of epinephrine administration on levels of pituitary cyclic AMP and plasma hormones. Rats were injected with saline or epinephrine bitartrate (1 mg/kg lP) and sacrificed by decapitation 1, 5, 15, 30 or 60 min post-injection. Levels of pituitary cyclic AMP and plasma ACTH, beta-endorphin, beta-LPH, corticosterone and prolactin were determined by radioimmunoassays. The injection procedure itself was somewhat stressful as demonstrated by increased levels of plasma prolactin and ACTH 5 min following either saline or epinephrine injection. This "stress" response was rapid and short-lasting for the pituitary hormones. The response of the adrenal hormone, corticosterone, to saline injection was slower in onset and longer in duration. Pituitary cyclic AMP levels did not increase following saline injection. Epinephrine-injected animals displayed markedly elevated plasma levels of ACTH, beta-endorphin and beta-LPH at 15, 30 and 60 min as compared to control or saline-injected rats. In addition, levels of pituitary cyclic AMP were increased over 10 fold at these times. Levels of plasma prolactin, a stress-responsive hormone, were not significantly increased in epinephrine-injected animals as compared to saline-injected rats indicating that these later responses seem to be specific to epinephrine rather than to stress.     

Effects of a dopaminergic stimulant,amfonelic acid,on anterior pituitary hormone release in conscious rats

The response of plasma LH, Prolactin, GH and TSH levels to systematic administration of a specific central dopaminergic stimulant, amfonelic acid (AFA), by intravenous pulse injection in ovariectomized (OVX) and OVX estrogen-progesterone primed conscious rats has been evaluated. Intravenous injection of 0.2 mg/kg of AFA had no influence on plasma LH concentration until 60 min after injection when it was significantly elevated. Increasing the dose to 1 mg/kg reduced LH titers at 15 and 30 min with a return to preinjection levels by 60 min. AFA produced a dose-dependent decrease in plasma prolactin levels; the decrease occurred as early as 5 min after injection. AFA, both at 0.2 and 1 mg/kg doses, was effective in producing a sharp, dose-related rise in plasma GH levels. By contrast, TSH levels were significantly suppressed by both doses of AFA. Injection of the 1 mg/kg dose of AFA did not modify plasma LH levels in OVX-steroid-primed animals, white producing a comparable effect on plasma prolactin, GH and TSH levels to that observed in OVX animals. The present results indicate that endogenously released DA can have profound effects on pituitary hormone release, inhibiting PRL and TSH discharge, stimulating GH release and either inhibiting or stimulating LH release.     

Prostaglandin F2α (PGF2α) and prolactin secretion in rats

Plasma prolactin and F-prostaglandins (PGF) were measured in anesthetized male Sprague-Dawley rats before and at 15, 30, 45 and 60 minutes following i.v. injection of either PGF_2α (4 mg/kg), chlorpromazine, 1 mg/kg or chlorpromazine (1 mg/kg) after pretreatment with i.p. indomethacin (2 mg/kg). Following PGF_2α administration, plasma prolactin levels increased significantly only at 15 and 30 minutes in spite of extremely high PGF levels throughout 60 minutes. Besides the expected rise in plasma prolactin, chlorpromazine caused a transient but statistically significant increase in PGF. Indomethacin blocked the chlorpromazine-induced PGF rise but not prolactin increase. Animals stressed with ether anesthesia showed elevation of plasma prolactin, which was not blocked by indomethacin although PGF concentration fell. These results indicate that PGF_2α can stimulate prolactin release. This effect does not appear to be physiologic since very high PGF levels are required. Furthermore, blockade of prostaglandin synthesis by indomethacin does not prevent the release of prolactin in response to chlorpromazine or stress. Our findings do not support a possible role of PGFs as intermediaries in prolactin release. However, it is possible that PGFs may work through other mechanisms not investigated in our study.     

The effect of ketamine hydrochloride anesthesia on basal and N-methyl-D,L-aspartate induced plasma prolactin secretion in the adult male rhesus monkey

The excitatory amino acids (EAAs), glutamate and aspartate, acting predominantly on N-methyl-D-aspartate (NMDA) receptor, have been shown to be involved in the central regulation of the secretion of several anterior pituitary hormones including prolactin (PRL), whereas ketamine hydrochloride (KH), a widely used anesthetic, has been reported to antagonize a variety of NMDA receptor mediated actions of these EAAs. In the present study, the effect of KH on basal PRL levels as well as on N-methyl-D,L-aspartate (NMA), an agonist of NMDA receptor, induced plasma PRL secretion was investigated in the adult male rhesus monkey. The values were compared to those obtained from the same animals restrained in primate chairs. The plasma PRL concentrations were higher in animals receiving KH administered either intramuscularly (2.5 mg/kg BW at 30 min intervals) or intravenously (10 mg/kg BW) as compared to those observed in the unanesthetized chair-restrained monkeys. NMA induced an unequivocal increase in plasma PRL concentrations in both conscious chair-restrained and KH anesthetized monkeys, but the response was greater in anesthetized animals than the conscious monkeys. The present findings suggest that KH has stimulatory effects on both basal and NMA induced plasma PRL secretion.     

Effect of buspirone and diazepam on cGMP level in the rat cerebellum

Diazepam at a dose of 5 and 10 mg/kg significantly decreases (by 50 and 60%, respectively) cGMP content 30 min following intraperitoneal injection to rats. Buspirone, at a dose of 2.5-25 mg/kg produced a nonsignificant (up to 18%) and at a dose of 50 mg/kg a statistically significant (p less than 0.05) 30% decrease in cerebellum cGMP content. Taking into account the identical anxiolytic effects of diazepam and buspirone, it is suggested that pharmacological effects of buspirone are not linked to the activation of GABA-ergic system.     

Effect of hyperthermia on the plasma concentrations of prolactin and cortisol in the fetal lamb and pregnant ewe during late gestation

Exposing pregnant sheep to an ambient temperature of 43 +/- 1 degree C for 8 h was associated with a 1-1.5 degrees C increase of maternal and fetal core temperatures, and a 11-fold and 3-5 fold increase in maternal and fetal plasma prolactin concentrations respectively. Hyperthermia did not change maternal or fetal plasma cortisol concentrations. We conclude that maternal and fetal hyperprolactinaemia may occur in late pregnancy during hyperthermic conditions and that the increase in fetal plasma prolactin is due to either increased secretion or decreased metabolic clearance of prolactin in the feto-placental compartment.     

Evaluation of oral administration of cortisol and metyrapone: the effects on serum cortisol in rainbow trout (Salmo gairdneri)

The effect of manipulating dietary levels of cortisol and metyrapone on peripheral concentrations of serum cortisol was examined in rainbow trout, Salmo gairdneri. Fish were fed 0, 10, 20, 30, 40 or 50 mg/kg body weight/day of metyrapone or cortisol for 7 days. All levels of cortisol tested increased peripheral levels of serum cortisol. Feeding a level of 30-40 mg/kg body weight/day of metyrapone depressed serum cortisol. We describe, herein, a noninvasive technique for suppression or stimulation of serum cortisol in rainbow trout.     

Changes in serum hormone and peptide levels in rats in experimental epilepsy

Serum levels of 7 hormones and neuropeptides were studied in the course of development of a generalized epileptic activity (EA) induced in rats by intraperitoneal administration of corasole (75 mg/kg), i.e. 30 s (latent period), 50-150 s, 5-10 min after epileptogenic administration. A significant increase in the levels of ACTH (5.2-fold), glucagon (1.8.-fold), angiotensin I and renin activity were shown to occur 90-180 s later. Further on in the course of EA the level of ACTH remained enhanced but the level of glucagon and renin-angiotensin activity returned to normal. The levels of cortisol, vasopressin and aldosterone were enhanced 2-3-fold 30 min later. The level of insulin 30 min later remained unchanged. The role of neuropeptides and hormones in the onset and suppression of EA is discussed.     

Endotoxaemia in rats: role of NO, PAF and TXA2 in pulmonary neutrophil sequestration and hyperlactataemia.

OBJECTIVE AND DESIGN: The involvement of PAF, TXA2 and NO in LPS-induced pulmonary neutrophil sequestration an hyperlactataemia was studied in conscious rats. As pharmacological tools WEB 2170 (PAF receptor antagonist, 20 mg/kg), camongarel (inhibitor of TXA2 synthase, 30 mg/kg), N(G)-nitro L-arginine methyl ester (L-NAME -- non-selective nitric oxide synthase inhibitor, 30 mg/kg) were used. METHODS: Plasma lactate and NO2-/NO3- levels as well as myeloperoxidase (MPO) activity in lung tissue were measured one and five hours after administration of LPS (4 mg/kg(-1)). RESULTS: LPS induced a twofold increase in plasma lactate levels and nearly 10-fold increase in plasma NO2-/NO3- levels five but not one hour after LPS administration. However, LPS-induced increase in pulmonary MPO activity was seen at both time intervals. Neither WEB 2170 nor camonagrel changed one or five hours responses to LPS (lactate, NO2-/NO3-, MPO). L-NAME potentiated LPS-induced rise in MPO activity in the lung and this potentiation was not affected by WEB 2170 or camonagrel. L-NAME supressed plasma NO2-/NO3- response and substantially potentiated plasma lactate response to LPS and both effects were partially reversed by WEB 2170 or camonagrel. CONCLUSIONS: In summary, we demonstrated that PAF and TXA 2 play a role in overproduction of lactate during endotoxaemia in NO-deficient rats. However, these lipids do not mediate endotoxin-induced sequestration of neutrophils in the lung.     

The failure of prolactin to initiate lactogenesis in the ewe.

Infusion of exogenous prolactin (NIH-P-S11) at 1 mg/h for 10 h into ewes pretreated for 30 days with oestradiol benzoate and progesterone was unable to initiate milk secretion. Similarly primed ewes injected with 10 microgram thyrotrophin releasing hormone also failed to lactate but all ewes injected with dexamethasone (10 mg daily for 5 days) after oestrogen plus progesterone treatment secreted copious quantities of milk. The results suggest that prolactin, itself, is not capable of initiating lactogenesis in the ewe.