John C. George

From Land to Water: the Origin of Whales, Dolphins, and Porpoises

Cetaceans (whales, dolphins, and porpoises) are an order of mammals that originated about 50 million years ago in the Eocene epoch. Even though all modern cetaceans are obligate aquatic mammals, early cetaceans were amphibious, and their ancestors were terrestrial artiodactyls, similar to small deer. The transition from land to water is documented by a series of intermediate fossils, many of which are known from India and Pakistan. We review raoellid artiodactyls, as well as the earliest families of cetaceans: pakicetids, ambulocetids, remingtonocetids, protocetids, and basilosaurids. We focus on the evolution of cetacean organ systems, as these document the transition from land to water in detail.

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).

Suppression of sympathetic nervous system by short photoperiod and melatonin in the Syrian hamster.

Exposure to short photoperiod or melatonin treatment brings about gonadal regression in Syrian hamsters. The possible influence of these treatments on the sympathetic nervous system (SNS) in these animals was investigated. Male Syrian hamsters were exposed to either long or short photoperiod or subjected to administration of melatonin or its vehicle solution. Exposure of hamsters to 10 weeks of short photoperiod, significantly reduced the noradrenaline (NA) turnover in the heart. Daily administration of melatonin for 8 weeks also resulted in a similar suppression of NA turnover in the heart. Hamsters that were treated with melatonin maintained a lowered metabolic rate as well, at and below thermoneutral temperature. These findings suggest that in a deep hibernator, short photoperiod could suppress the peripheral sympathetic activity and that melatonin may act as the endogenous mediator.

Glycogen utilization by the white fibres in the pigeon pectoralis as main energy process during shivering thermogenesis.

Abstract 1. 1. The importance of intramuscular glycogen stores as metabolic fuel for shivering thermogenesis was studied in the pectoralis muscle of the pigeon exposed to cold (−25°C; 30 min). 2. 2. Exposure of partially defeathered pigeons, unlike that of fully plumed ones, elicited an intensely vigorous shivering response which resulted in a rapid depletion of the glycogen reserves in the white fibres, but not in the red. 3. 3. No marked loss of intracellular glycogen was noted when the shivering response was impaired by curarization, denervation or tendotomy of the muscle. 4. 4. It is concluded that the white glycogen-utilizing fibres, unlike the red fat-utilizing ones, are functionally adapted for “fast-twitch” activity and selectively called upon when brief but vigorous bouts of muscular shivering are required to raise body temperature.

Diurnal and seasonal variation in liver glycogen and fat in relation to metabolic status of liver and M. pectoralis in the migratory starling, Sturnus roseus, wintering in India

1. Levels of glycogen and fat in the liver showed a diurnal difference, being higher at dusk than at dawn during the post- and premigratory periods. 2. Fat level increased by at least more than double from its lowest in the postmigratory period (August) to highest towards migration time (21-30 April) at both dawn as well as dusk. 3. With the steady increase in liver fat, there was a gradual decrease in liver glycogen up to about the middle of April and a slight increase thereafter. 4. RQ values obtained for liver and pectoralis muscle slices in vitro at postmigration (August) indicated lipid utilization. Those for the premigratory period indicated hyperlipogenesis, while towards migration time the values denoted carbohydrate catabolism and sparing of lipid.

Influence of exogenous growth hormone and its antiserum on plasma free fatty acid level in the pigeon

Abstract 1. 1. Intramuscular injection of ovine growth hormone (GH) into pigeons produced a highly significant increase in the plasma free fatty acid (FFA) level when assayed 3 hr after the injection. 2. 2. Injection of anti-GH serum failed to produce a significant change in the FFA level; the normal endogenous rhythm of plasma FFA remained about the same after the injection. 3. 3. Injection of anti-GH serum did suppress the endogenous plasma GH level at first (8 hr after injection), but this effect disappeared later (26 hr after injection); the normal endogenous rhythm of plasma GH was, however, adversely altered subsequent to the antiserum injection. 4. 4. It is suggested that, while the endogenous GH was inhibited, some other lipolytic agent(s) (hormone(s)) mediated the elevation of plasma FFA level.

Influence of glucagon and neurohypophysial hormones on plasma free fatty acid levels in the pigeon

Abstract 1. 1. The effect of intravenous injections of vasopressin, oxytocin, vasotocin and glucagon on the plasma free fatty acid (FFA) level was studied in the pigeon. 2. 2. The plasma FFA level in pigeons during winter was found to be higher than that in the fall. 3. 3. Vasopressin caused a decline and oxytocin a slight increase in plasma FFA at 15 min post-injection. Vasotocin brought about a highly significant increase at 30 min. Glucagon produced a marked increase in 5 min and when followed by vasotocin, a further increase was obtained. 4. 4. The possible significance of the lipolytic action and lipid mobilization, of oxytocin and vasotocin in bird migration, is discussed in the light of the release of the neurohypophysial neurosecretory material prior to migration reported earlier in two passerine migrants.

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.

Fine structure and metabolic adaptation of red and white muscles in tuna

SynopsisAn electron microscopic study of the red and white muscle fibres in the trunk musculature of the Kawakawa tuna (Euthynnus affinis) was carried out with a view to correlating their structure with metabolic adaptation. The red fibres which are considerably smaller in diameter (34.58 μm ± 6.16 S.D.) are characterized by their high content of myoglobin, mitochondria, lipid droplets and glycogen granules. The white fibres which are relatively larger in diameter (66.03 μm ± 11.59 S.D.) are characterized by their lack of myoglobin, low mitochondria) density, high content of glycogen granules and the conspicuous absence of lipid droplets. The characteristics in fine structure of the two fibre types are discussed in the light of their metabolic adaptation, the red fibres as being adapted for long term cruising movement utilizing lipid as the main source of energy and the white fibres for short bursts of activity metabolizing glycogen as the chief fuel.The tuna, with the acquisition of the counter-current heat exchange system which provides for the retention of the heat generated from high substrate oxidation in the red muscle and an efficient respiratory system, it is postulated, is well adapted for high speed sustained swimming.