T.M. John

Circadian rhythm of plasma prolactin, growth hormone, glucose and free fatty acid in juvenile kokanee salmon, Oncorhynchus nerka

Abstract 1. 1. Plasma levels of prolactin and growth hormone in Oncorhynchus nerka show a marked circadian rhythm. 2. 2. High levels of both hormones are found during the dark phase of the photoperiod (03.00 hours to 06.00 hours for prolactin and 24.00 hours to 03.00 hours for growth hormone). 3. 3. Low values for prolactin were found between 12.00 hours and 16.00 hours and for growth hormone at 15.00 hours. 4. 4. A second “surge” of growth hormone may also be present at 12.00 hours. 5. 5. Plasma FFA levels were high during the morning hours (09.00 hours to 12.00 hours). Plasma glucose levels did not vary significantly at any time period. 6. 6. The possible involvement of prolactin and/or growth hormone in lipid mobilization in O. nerka is discussed.

The effect of growth hormone and prolactin on the mobilization of free fatty acids and glucose in the kokanee salmon, Oncorhynchus nerka.

Abstract 1. 1. Three experiments were undertaken to investigate the involvement of growth hormone and prolactin in the mobilization of lipids and carbohydrates in kokanee salmon. 2. 2. Deprivation of food caused a drop fn plasma free fatty acids (FFA), liver glycogen and muscle water content. 3. 3. Enforced exercise for a period of 24 hr caused a rise in plasma growth hormone and prolactin. 4. 4. Injections of growth hormone or prolactin caused a rise in muscle FFA and a decrease in muscle water content.

Influence of chronic melatonin implantation on circulating levels of catecholamines, growth hormone, thyroid hormones, glucose, and free fatty acids in the pigeon

Subcutaneous implantation of melatonin pellets (2 mg melatonin + 30 mg beeswax) for a period of 12 weeks, with reinforcement of implants every 2 weeks, caused significant increases in plasma levels of glucose and growth hormone (GH). Plasma levels of thyroxine (T4) were lower and the triiodothyronine (T3)/T4 ratio was higher in the melatonin-treated pigeons. However, melatonin treatment produced no significant effect on plasma levels of free fatty acids (FFA), T3, epinephrine (E), and norepinephrine (NE), although trends (P greater than 0.05) toward slight increases in FFA and T3 and decreases in E and NE were apparent. Since melatonin treatment caused increases in the levels of plasma glucose and GH and not in those of the other substances measured, it is suggested that melatonin enhances carbohydrate metabolism in preference to lipid metabolism in resting pigeons during the day (photophase) when pineal and circulating levels of melatonin are normally lower than during night (scotophase).

Circadian rhythm of plasma growth hormone levels in the pigeon

Abstract The plasma growth hormone (GH) level in the pigeon was assessed by radioimmunoassay during a 24‐hr period of 12‐hr light (photophase) and 12‐hr dark (scotophase). The peak GH level was found to be at 06.00 hr (toward the end of the scotophase or onset of the photophase). Thereafter it dropped to its lowest at 18.00 hr (end of the photophase), thus revealing the existence of a circadian rhythm. This rhythm in plasma GH concentration has been correlated with a corresponding free fatty acid rhythm in the pigeon. Diurnal changes, free fatty acid levels, lipid mobilization, muscular activity, plasma growth hormone, starvation.

Blood levels of thyroid hormones and certain metabolites in relation to moult in the harp seal (Phoca groenlandica)

1. Changes in blood levels of thyroxine (T4), triiodothyronine (T3), free fatty acids (FFA), glucose, pyruvic acid and lactic acid in the harp seal during moult, were studied. 2. Serum levels of both T4 and T3 showed significant increase in the moult phase from that in the pre-moult phase. While T4 level continued to remain high during the early and late post-moult phases, T3 level dropped in the latter two phases to the same low pre-moult level. 3. The T3/T4 ratio was significantly higher during the pre-moult phase than that in all the other phases. It is suggested that the high pre-moult T3/T4 ratio marks the initiation of moult. 4. There were no significant changes in the levels of the metabolites studied except that of FFA which was highest in the moult phase indicating the hormonal basis of lipid mobilization.

Circadian rhythm of free fatty acid levels in plasma and pectoralis muscle of the pigeon

Abstract The levels of free fatty acids (FFA) in the plasma and pectoralis muscle were studied in the pigeon under a 12‐hr photoperiod at 25 C. The plasma FFA level was found to be at its peak in the middle of the scotophase and low at the end of the same phase, while the muscle FFA level registered a rise reaching the peak at the end of this phase to drop to the low towards the middle of the photophase. In the light of these observations, the existence of a circadian rhythm in the FFA levels of the plasma and pectoralis muscle in the pigeon, is suggested.

Effect of vasotocin on plasma free fatty acid level in the migrating anadromous sea lamprey

The effect of injections of arginine vasotocin (AVT) on plasma free fatty acid (FFA) levels was studied in anadromous sea lampreys collected in the St. John River, New Brunswick, during their upstream spawning migration. Plasma FFA was significantly higher in lampreys injected with a single dose of 1 000 mU vasotocin/kg body weight than in those receiving only the vehicle solution, the difference being the greater at 90 than at 30 min post-injection. The significance of AVT in migration is discussed.

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.

Diurnal thermal response to pinealectomy and photoperiod in the pigeon

Abstract An increase in body temperature (Tb) observed in pinealectomized (Px) early winter pigeons as opposed to sham‐operated (SPx) ones, at two as well as three weeks post‐surgery, was found to have disappeared when examined one year later during corresponding season. Following this one‐year post‐surgery period under 12‐h daily photoperiod and 25°C ambient temperature (Ta), neither a 3‐week exposure to continuous light nor a 1‐week exposure to continuous darkness was found to produce any difference in Tb between Px and SPx pigeons. In pigeons (Px, SPx/Normal) maintained on a 12‐h daily photocycle, and 25°CTa, the diurnal Tb rhythm of being high during photophase and low during scotophase was observed in all the seasons studied. Under continuous light as well as continuous darkness, however, the diurnal Tb rhythm was found to be effaced. Seasonal variations in Tb were observed in response to pinealectomy. Summer Px pigeons showed no significant hyperthermia whereas early winter, mid‐winter and fall pige...

Effect of vasotocin and glucagon on plasma growth hormone levels in the pigeon

Abstract 1. 1. Injection of vasotocin did not have a significant effect on the plasma growth hormone (GH) level in the pigeon, at 15 or 30 min post-injection, when compared with isotonic saline injection. 2. 2. GH levels at 30 min post-injection of vasotocin as well as of saline were significantly higher than the respective levels at 15 min post-injection. 3. 3. Glucagon produced an elevation in plasma GH at 5 min post-injection. 4. 4. Injection of vasotocin 5 min after the glucagon injection produced a further significant increase in plasma GH when tested 15 min after the vasotocin injection (i.e. 20 min after glucagon injection). No such increase was noticed when saline alone was injected instead of vasotocin. 5. 5. A synergistic effect of glucagon and vasotocin on plasma GH level has been suggested.