Effect of vagotomy on plasma levels of growth hormone, free fatty acids and glucose in the pigeon

Plasma levels of growth hormone (GH), free fatty acids (FFA) and glucose were measured in vagotomized (VgX) and sham-operated (VgS) control pigeons. In VgX pigeons, GH level was significantly lower whereas FFA and glucose levels were higher than in VgS pigeons. The depression in GH level in VgX pigeons has been attributed to the significantly high levels of norepinephrine (NE) and corticosterone in these Birds. The higher plasma FFA concentration in VgX pigeons was therefore due to adipokinetic hormonal action other than of GH. It has been suggested that the adrenocorticotrophic hormone (ACTH) and/or NE could have produced the increase in plasma FFA in VgX pigeons. The pronounced hyperglycemia seen in VgX pigeons has been attributed to catecholamine action in the absence of the vagal tone.     

Seasonal changes in some plasma hormones in pigeons: diurnal variation under natural photoperiods with constant or seasonally changing ambient temperature

The diurnal variations of several plasma hormones and free fatty acids (FFA) were studied during periods in summer and winter for pigeons reared either outdoors or indoors. The latter were subjected to constant temperature and naturally varying photoperiods. A significant seasonal variation in the mean daily levels of triiodothyronine (T3), thyroxine (T4), corticosterone (B), lutropin (LH) and FFA was seen in the outdoor birds and in the T4 and B levels of indoor birds. The diurnal variation of hormone levels was generally more pronounced in winter in both groups. Cold ambient temperature significantly decreased the plasma LH level and potentiated the increasing effect of short photoperiod on plasma B level. Diurnal variation of plasma FFA level seems to be under the control of photoperiod, without any effects due to the ambient temperature. No significant correlation was found between FFA and GH concentrations.     

Growth hormone response to human pancreatic growth hormone releasing factor in cattle

The effects of a growth hormone releasing factor, human pancreatic growth hormone releasing factor-44 (hpGRF-44), on growth hormone (GH) secretion in calves, heifers and cows were studied. A single intravenous (iv) injection of 0.1, 0.25, 0.5 or 1.0 microgram of synthetic hpGRF-44 per kg of body weight (bw) in calves significantly elevated the circulating GH level within 2-5 min, while no increase in plasma GH was observed in saline injected control calves. The plasma GH level increased proportionally to the log dose of hpGRF-44, and reached a peak at 5-10 min (p less than 0.01). Subcutaneous injection of hpGRF-44 also elevated the plasma GH level, but the peak value at 15 min was 37% of that of iv injection (p less than 0.05). Intravenous injection of 0.25 microgram of hpGRF-44 per kg of bw to female calves, heifers, and cows significantly elevated mean the GH levels from 8.5, 2.3, and 1.6 ng/ml at 0 time to peak values of 97, 26, and 11.6 ng/ml, respectively (p less than 0.01). The plasma GH response and basal level in calves were significantly higher than those of heifers or cows (p less than 0.025). The plasma GH response to hpGRF-44 as well as the basal level decreased with advancing age. The plasma GH response to hpGRF-44 and basal GH in male calves were significantly greater than those in female calves (p less than 0.001). These results indicate that synthetic hpGRF-44 is a potent secretogogue for bovine GH, and suggest its usefulness in the assessment of GH secretion and reserve in cattle.     

Studies of growth hormone secretion in juvenile diabetes.

To further investigate the GH secretion in juvenile diabetics, blood glucose (BG) and plasma growth hormone (GH) were determined during controlled exercise performed in basal condition and under glucose infusion, in 7 controls and 22 juvenile diabetics aged 12--35 years, 10 of them with fundal vascular lesions. In controls, glucose infusion significantly lowered the exercise induced GH rise observed under basal conditions. In diabetics, under basal conditions, diabetics with low basal BG (BG less than 100 mg/100ml) had higher GH secretion than those with high basal BG (BG greater than 140 mg/100 ml; p less than 0.05). Under glucose infusion, diabetics with normal BG peak values (not different from controls: BG = 284 +/- (SK) 45 mg/100 ml) had significantly higher plasma GH levels than controls (p less than 0.01). In contrast, in diabetics with BG peak value higher than controls (BG greater than 374 ng/100 ml), plasma GH levels were not different from control values. This study indicates that exercise induced GH secretion in diabetics is mainly related to actual BG levels. Furthermore, we found no relation between the magnitude of GH secretion and the presence of retinopathy in diabetics.     

Serum glucose and free fatty acids modulate growth hormone and luteinizing hormone secretion in the pig

Two experiments were conducted to determine the effect of free fatty acids (FFA) and glucose treatment on growth hormone (GH) and luteinizing hormone secretion in the pig. In Experiment (Exp) 1, 15 prepuberal gilts received an intravenous infusion of FFA (n = 5; 3 ml of 10% Liposyn II/kg), glucose (n = 5; 1 g/kg), or saline (n = 5; 3 ml of 0.9%/kg). Jugular blood samples were collected every 15 min for 2 hr before and 3 hr after intravenous infusion of saline, FFA, and glucose. Synthetic [Ala15]-h growth hormone-releasing factor-(1-29)NH2 (1 microgram/kg) and gonadotropin-releasing hormone (0.2 micrograms/kg) were administered 30 min after infusion (Time 0 = infusion). In Exp 2, eight prepuberal gilts received either FFA (n = 4) or saline (n = 4) as described in Exp 1, except that treatments were given every hour ove a 10-hr period. Blood samples were collected every 15 min from 1 hr before to 10 hr after the start of FFA or saline infusion. In Exp 1, the peak GH response to growth hormone-releasing factor was delayed by 45 min (P less than 0.01) by glucose treatment and suppressed (P less than 0.01) by FFA treatment. The luteinizing hormone response to gonadotroph-releasing hormone was suppressed (P less than 0.03) by glucose and enhanced (P less than 0.03) by FFA. In Exp 2, the number of GH pulses was increased (P less than 0.05) by FFA infusion and GH concentrations were positively correlated (r = 0.58, P less than 0.0003) with FFA concentrations, while luteinizing hormone pulse amplitude was greater (P less than 0.01) in FFA gilts than in saline gilts. These results indicate that FFA are more effective modulators of GH secretion than acute hyperglycemia, while metabolic status can alter pituitary responsiveness to gonadotropin-releasing hormone.     

Flight effects on plasma levels of free fatty acids, growth hormone and thyroid hormones in homing pigeons

Significant increases in circulating levels of free fatty acids (FFA) and growth hormone (GH), were observed in homing pigeons after a flight of 48 km, lasting 60-80 min. No significant change in plasma levels of thyroxine (T4) and triiodothyronine (T3) was observed. Nor was there any change in T3/T4 ratio. The increase in plasma FFA is attributed to the increased release into circulation of at least one adipokinetic hormone, GH. It may be concluded that in free sustained homing flight under normal weather conditions and within the specific distance and duration, metabolic fuel and hormonal homeostasis is maintained.     

Muscle type dependent increase in intramyocellular lipids during prolonged fasting of human subjects: a proton MRS study.

The amount of intramyocellular lipids in skeletal muscle was assessed by proton magnetic resonance spectroscopy during a voluntary fasting period of 120 h in four healthy lean volunteers. The aim of the study was to determine whether muscular lipid uptake in the presence of high plasma lipid levels, or lipid oxidation due to lacking glycogen as a source of energy in musculature, are the dominant effects on intramyocellular lipid levels under fasting conditions in various muscle types. Intramyocellular lipids were quantified in the tibialis anterior (mixed type I and type II fibers, predominantly type II) and the soleus muscle (predominantly type I fibers) before and after 24 h, 72 h, and 120 h of fasting. An extreme increase in intramyocellular lipids to levels of 369 % (median) was found in the tibialis anterior muscle compared to baseline value (intramyocellular lipid level prior to fasting, set to 100 %; p = 0.02). The soleus muscle with clearly higher baseline content of intramyocellular lipids (2 - 4-fold compared to tibialis anterior) revealed slightly delayed and less pronounced uptake of intramyocellular lipids during fasting to 152 % (median) after 120 h (p = 0.02). The absolute increment in intramyocellular lipids (in terms of ratios between lipid and creatine signals) was also higher in tibialis anterior than in soleus (not statistically significant). These findings indicate augmentation of the intramyocellular lipid pool during long-term elevation of plasma FFA in the presence of low plasma insulin concentrations in both muscles investigated. The rate of muscular lipid oxidation during fasting is clearly lower than the increased uptake of FFA by myocytes.     

Twenty-four hour plasma GH, FSH and LH profiles in patients with Turner's syndrome

We studied the plasma GH profiles in 6 patients with Turner's syndrome and 6 normal girls of short stature by sampling every 20 min for 24 hours. We observed episodic secretion of GH in these subjects. The mean plasma 24 h GH level in patients with Turner's syndrome was 3.6 +/- 1.4 (SD) ng/ml which was significantly lower than that of normal short girls (7.1 +/- 2.2 ng/ml, p less than 0.01). The GH secretion during both nighttime and daytime was decreased in the patients with Turner's syndrome, however the number of pulses did not differ significantly. There were no correlations between the mean plasma 24 h GH level on one hand and peak GH level obtained after GH provocative test and plasma somatomedin C on the other. Plasma FSH and LH levels were also measured in 4 patients with Turner's syndrome. Both levels were elevated and there observed no clear pulsatile secretion of FSH, but, some pulsatile secretion of LH was observed in two patients. These data indicate that patients with Turner's syndrome have decreased endogenous GH secretion, even though they show normal GH responses to GH provocative tests.     

Study of insulin-like growth factor I in human obesity.

In obesity there is a decrease in basal and stimulated GH secretion. IGF-I, which has negative feedback effects on GH secretion, could be the initial mediator of such alterations. We studied IGF-I levels in obese subjects and their relationship to the obesity level and GH secretion. We determined plasma IGF-I, basal and stimulated GH in 30 normal and 30 obese women and related these variables to obesity indices (body mass index, BMI, and % overweight). Baseline plasma GH values were 1.2 +/- 0.3 and 2.3 +/- 0.6 micrograms/l in obese subjects and controls, respectively (NS). Mean peak GH secretion after stimuli were 11.2 +/- 1.4 and 34.4 +/- 5.6 micrograms/l in obese subjects and controls, respectively (p less than 0.001). Plasma IGF-I were 1.0 +/- 0.1 U/ml and 0.7 +/- 0.1 U/l in obese subjects and controls, respectively (NS). There was a significant negative correlation between plasma IGF-I and age (r = -0.55, p less than 0.001) and a significant negative correlation between mean peak GH secretion and weight (r = -0.60, p less than 0.001), BMI (r = -0.64, p less than 0.001) and percentage of ideal body weight (r = -0.67, p less than 0.001). We did not find any correlation between IGF-I and indices of overweight. These data suggest that the reduced GH secretion found in obesity is not related to a negative feedback inhibition by elevated levels of IGF-I and that adiposity is not associated with a decline in IGF-I levels. We confirm the existence of a negative correlation between GH secretion and obesity indices.     

Effects of age on fasting-induced changes in insulin, glucose, urea nitrogen, and free fatty acids in sera of sheep

The hypothesis that prepubertal ewe lambs are metabolically different from postpubertal ewes was tested. Ovariectomized ewes (4 years of age; n = 4) and lambs (6 months of age; n = 4) were fasted for 72 hr. Serum concentrations of insulin, glucose, urea nitrogen, and free fatty acids (FFA) were measured in blood samples taken at 6-hr intervals between 30 hr before and 72 hr after feed removal. Serum concentrations of urea nitrogen and glucose were not different (P greater than 0.20) between age groups before fasting. Serum concentrations of insulin in ewes increased toward the end of the prefast period whereas those in lambs did not (age x time, P less than 0.01). Serum concentrations of FFA in ewes tended to be lower (P less than 0.07) than those in lambs prior to fasting. During fasting, concentrations of insulin decreased (P less than 0.02) over time in ewes and lambs and did so in a similar manner (age x time, P greater than 0.70). Urea nitrogen increased (P less than 0.0001) in both fasted ewes and fasted lambs in a comparable manner (age x time, P greater than 0.20). Concentrations of glucose during fasting were not significantly affected (P greater than 0.90) by age. There was a tendency (P = 0.08) for concentrations of glucose to change over time but the pattern did not appear to be related to fasting. During fasting, concentrations of FFA tended to be higher (P less than 0.07) in lambs than in ewes and increased (P less than 0.0001) in both groups in a similar fashion (age x time, P greater than 0.10). The findings herein suggest that turnover of FFA in lambs may be slightly greater than that in ewes during the fed and fasted states.     

Effects of growth hormone-releasing factor and somatostatin on growth hormone secretion in hypophysial stalk-transected beef calves

The effects of growth hormone-releasing factor (GHRF) on growth hormone (GH) secretion were studied in beef calves after hypophysial stalk transection (HST). Peripheral GH concentration during surgery was elevated for 60 min after the initiation of anesthesia to 15 ng/ml, which was greater than plasma levels after HST and during the recovery period (0-30 hr mean, 3 ng/ml; P less than 0.05). Episodic GH secretion normally seen in sham-operated controls (SOC) was abolished after HST. Before HST, calves responded to 80% of the GHRF challenges, whereas after HST calves responded to every challenge of GHRF with an increase in plasma GH. A dose of 0.067 microgram human pancreatic (hp) hpGHRF(1-40)OH/kg body wt 3 days after HST increased plasma GH to 55 ng/ml from a control period mean of 5 ng/ml (P less than 0.04). On Day 8, HST calves received two injections of 0.067 microgram hpGHRF/kg body wt at 3-hr intervals, with feeding 70 min after the first injection. During two preinjection control periods, basal GH averaged less than 4 ng/ml and increased to 17 (P less than 0.02) and 9 (P less than 0.04) ng/ml immediately after the first and second injection of hpGHRF, but the response declined over the 8-day period after surgery. On Days 19 and 20, the HST calves were infused iv with 0.033 and 0.067 microgram somatostatin(SS)-14 (SRIH)/kg body wt, during which a pulse injection of 0.067 microgram hpGHRF/kg body wt was administered. GH increased to 9 and 5 ng/ml during the 0.033- and 0.067-microgram SRIH infusions after GHRF; no somatotropic rebound was observed after the SRIH was discontinued as was seen in the animals while the hypothalamic-hypophysial connections were intact. Five and six months after HST the responses to two analogs of rat hypothalamic GHRF were similar to those in SOC calves. These results indicate that HST calves responded to exogenous GHRF with an abrupt increase in plasma GH, but GH response to GHRF during SRIH infusion was greatly inhibited.     

Growth hormone, thyrotropin and prolactin responses to simultaneous administration of human growth hormone-releasing factor and thyrotropin releasing hormone in the bovine

The effects of intravenous injection of synthetic human pancreatic growth hormone-releasing factor-44-NH2 (hpGRF-44) and synthetic thyrotropin releasing hormone (TRH), or hpGRF-44 in combination with TRH on growth hormone (GH), thyrotropin (TSH), and prolactin (PRL) release in dairy female calves (6- and 12-month-old) were studied. When 0.25 microgram of hpGRF-44 per kg of body weight (bw) was injected in combination with TRH (1.0 microgram per kg of bw), the mean plasma GH concentration of the 12-month-old calves rose to a maximum level of 191.5 ng/ml (P less than 0.001) at 15 min from the value of 6.8 ng/ml before injection at 0 min. The maximum level was 3.1 and 6.1 times as high as the peak values obtained after injection of hpGRF-44 (0.25 microgram per kg of bw) and TRH (1.0 microgram per kg of bw), respectively (P less than 0.001). The area under the GH response curve for the 12-month-old calves for 3 hr after injection of hpGRF-44 in combination with TRH was 2.5 times as large as the sum of the areas obtained by hpGRF-44 and TRH injections. In contrast, the mean plasma GH level was unchanged in saline injected calves. The magnitudes of the first and the second plasma GH responses in the 6-month-old calves to two consecutive injections of hpGRF-44 in combination with TRH at a 3-hr interval were very similar. The peak values of plasma GH in the calves after hpGRF-44 injection were 2-4 times as high as those after TRH injection.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth hormone-releasing factor on growth hormone secretion in prepubertal calves

The effects of iv administration of growth hormone-releasing factor (GRF) on growth hormone (GH) release and on nitrogen metabolism were measured in prepubertal calves. Crossbred beef heifers (111 kg) were used in a Latin square design to test the effects of 0, 0.01, 0.033, 0.067, and 0.1 microgram human pancreatic (hp) GRF [hpGRF (1,40)OH]/kg body wt on plasma GH concentrations. When they were given doses of 0.067 and 0.1 microgram hpGRF/kg body wt, plasma GH increased (P less than 0.05) within 5-15 min, compared with injections of control buffer, and then returned to preinjection concentrations. The response to 0.067 microgram hpGRF/kg body wt every 3 hr for 42 hr was studied in five heifers (137 kg body wt). The animals responded to 50% of the GRF injections with an increase in plasma GH during every 6-hr period measured. Nitrogen retention, hormone concentrations, and weight gain were measured in five bull calves (90 kg body wt) administered 0 or 0.067 microgram Nle rat hypothalamic GRF (1,29)NH2/kg body wt every 4 hr for 10 days. Metabolic parameters were interpreted to indicate an anabolic response to GRF even though increases of 16% in nitrogen retention, 23% in plasma somatomedin C concentrations, and 36% in weight gain with pulsatile GRF treatment were variable and statistically similar to those of controls. These results indicate that GRF induces peak GH secretion within 15 min in prepubertal calves and that calves can respond to multiple injections of GRF with an increase in plasma GH.     

Effects of human growth hormone on erythrocyte insulin binding in growth hormone deficient children

In this paper, the effect of acute human growth hormone (GH) administration on erythrocyte insulin binding in GH deficient children (N = 6) was studied. Following GH (0.25 U/kg) administration, the blood levels of GH peaked within 4 to 8 h and returned to basal levels 24 h later. However, the changes in somatomedin activity, free fatty acid (FFA), urea, blood glucose and 125I-insulin binding to erythrocyte were observed around 24 h following the injection, and there was a converse relationship between maximum percent 125I-insulin binding (IBmax) and FFA (P less than 0.02). By Scatchard analysis it was found that the decrease in IBmax is mainly due to the change in the number of insulin receptors. These results suggest that GH may possibly affect the insulin binding to erythrocyte indirectly through metabolic changes as a result of hormonal changes in GH deficient children.     

The inter- and intra-subject variabilities of plasma GH response to human growth hormone-releasing hormone (1-44) NH2 in men

The effects of intravenously given human growth hormone-releasing hormone (1-44) NH2 (hGRH-44) on growth hormone (GH) secretion were studied in normal men. A wide variability of intersubject GH response to hGRH-44 was observed. The peak plasma GH levels in response to 50, 100 and 200 micrograms hGRH-44 in 7 normal men were 9.1 +/- 3.2 ng/ml (Mean + SEM), 19.3 +/- 3.3 ng/ml and 22.4 +/- 4.0 ng/ml, respectively. Both the mean peak values for plasma GH response to 100 and 200 micrograms were significantly greater than that for 50 micrograms hGRH-44 injection (p less than 0.01), although there was no significant difference of the mean peak plasma GH values and mean concentrations at each time point, except for those at 120 min, when 100 or 200 micrograms hGRH-44 was administered. A significant difference in the mean amount of plasma GH secreted in response to hGRH-44 was observed only between 50 and 200 micrograms hGRH-44 injection (p less than 0.01). Furthermore, a dose-related plasma GH increase in response to hGRH-44 was not always observed in each subject. In contrast to the wide intersubject variability, the difference among responses of plasma GH to 100 micrograms or 200 micrograms of hGRH-44 given at multiple times separated by intervals of at least 1 week in each individual was relatively small.(ABSTRACT TRUNCATED AT 400 WORDS)     

Role of vasoactive intestinal polypeptide (VIP) in regulating the pituitary function in man

Intramuscular injection of synthetic VIP (200 micrograms) resulted in a rapid increase in plasma prolactin (PRL) concentrations in normal women, which was accompanied by the 4- to 7-fold increase in plasma VIP levels. Mean (+/- SE) peak values of plasma PRL obtained 15 min after the injection of VIP were higher than those of saline control (28.1 +/- 6.7 ng/ml vs. 11.4 +/- 1.6 ng/ml, p less than 0.05). Plasma growth hormone (GH) and cortisol levels were not affected by VIP in normal subjects. VIP injection raised plasma PRL levels (greater than 120% of the basal value) in all of 5 patients with prolactinoma. In 3 of 8 acromegalic patients, plasma GH was increased (greater than 150% of the basal value) by VIP injection. In the in vitro experiments, VIP (10(-8), 10(-7) and 10(-6) M) stimulated PRL release in a dose-related manner from the superfused pituitary adenoma cells obtained from two patients with prolactinoma. VIP-induced GH release from the superfused pituitary adenoma cells was also shown in 5 out of 6 acromegalic patients. VIP concentrations in the CSF were increased in most patients with hyperprolactinemia and a few cases with acromegaly. These findings indicate that VIP may play a role in regulating PRL secretion in man and may affect GH secretion from pituitary adenoma in acromegaly.     

Variations in plasma melatonin levels of the rainbow trout (Oncorhynchus mykiss) under various light and temperature conditions

Daily variations in plasma melatonin levels in the rainbow trout Oncorhynchus mykiss were studied under various light and temperature conditions. Plasma melatonin levels were higher at mid-dark than those at mid-light under light-dark (LD) cycles. An acute exposure to darkness (2 hr) during the light phase significantly elevated the plasma melatonin to the level that is comparable with those at mid-dark, while an acute exposure to a light pulse (2 hr) during the dark phase significantly suppressed melatonin to the level that is comparable with those at mid-light. Plasma melatonin kept constantly high and low levels under constant darkness and constant light, respectively. No circadian rhythm was seen under both conditions. When the fish were subjected to simulative seasonal conditions (simulative (S)-spring: under LD 13.1:10.9 at 13 degrees C; S-summer: under LD 14.3:9.7 at 16.5 degrees C; S-autumn: under LD 11.3:12.7 at 13 degrees C; S-winter: under LD 10.1:13.9 at 9 degrees C), melatonin levels during the dark phase were significantly higher than those during the light phase irrespective of simulative seasons. The peak melatonin level in each simulative season significantly correlated with temperature but not with the length of the dark phase employed. In addition, the peak melatonin level in S-autumn was significantly higher than those in S-spring although water temperature was the same under these conditions. These results indicate that the melatonin rhythm in the trout plasma is not regulated by an endogenous circadian clock but by combination of photoperiod and water temperature.     

Flight effects on plasma levels of lipid, glucagon and thyroid hormones in homing pigeons

Significant increases in the concentration of plasma glucagon-like immunoreactivity (GLI) and plasma levels of free fatty acids (FFA) and triglycerides (TG) concomitant with decreases in circulating levels of thyroxine (T4) and triiodothyronine (T3) and T3/T4 ratio were observed in homing pigeons, untrained for 3 months, after a flight of 48 km lasting 90-160 min. The increased level of FFA is attributed to glucagon stimulated lipolysis. The elevation of TG levels may be due to altered partitioning and utilization of lipoprotein in adipose tissue and muscle. Reductions in plasma T4, T3 and T3/T4 ratio are probably due to inhibition of T4 secretion and 5'-monodeiodination with possible conversion of T4 to reverse T3 (rT3). These processes may represent a mechanism for regulation of thyroid hormone metabolism during strenuous and extended flight.     

Sympathetic hyperreactivity in offspring of essential hypertensive patients

A multistage exercise test was carried out in normotensive subjects with normotensive parents (controls; n = 12), and 32 offspring of essential hypertensive patients that were normotensive (NTO; n = 20) or borderline hypertensive (BHO; n = 12) The groups were comparable as to age, weight and working capacity. Changes in sympathetic nervous activity were determined by measurements of plasma noradrenaline. The initial rise in noradrenaline levels during the exercise test was proportional to the increase in work load until the noradrenaline concentration rose sharply to levels more than 1000 pg/ml above baseline levels. The work load immediately prior to the steep rise in plasma noradrenaline (sympathetic threshold level: STL) is considered to represent the point from which anaerobic energy-yielding processes play an increasingly greater role as the work load increases. The initial increase in plasma noradrenaline until STL was significantly higher in both the NTO (p less than 0.02) and BHO (p less than 0.005) compared to the control group. The absolute noradrenaline level at STL and the increase in noradrenaline from baseline to STL were significantly higher in the BHO group (p less than 0.02, p less than 0.005). No significant differences between the groups were found when comparing noradrenaline levels at rest or at absolute or relative work loads. The systolic blood pressure response during the exercise test was significantly more pronounced in the BHO group (p less than 0.05) compared to the controls and the NTO group.     

Effect of thermal stress and dehydration on plasma levels of glucose, free fatty acids and growth hormone in the pigeon.

Pigeons were subjected to high ambient temperature and water deprivation for 3 days (28 degrees C, 31 degrees C and 36.5 degrees C respectively). After 3 days of heat stress and dehydration, the plasma levels of glucose, free fatty acids (FFA) and growth hormone (GH) were measured. Although the level of plasma glucose was not significantly altered, FFA and GH were found to be significantly increased. The possible mediation of the neurohypophysial hormone, vasotocin, in the syndhronous rise in plasma GH and FFA, is suggested.