Zvi Glick

Sodium potassium dependent ATPase in hypophysectomized rats: Response to growth hormone, triiodothyronine, and cortisone

Groups of hypophysectomized rats were treated with pharmacologic doses of growth hormone, triiodothyronine or cortisone acetate alone or with a combination of growth hormone plus triiodothyronine or growth hormone plus cortisone. After a 7 day period of treatment the hydrolysis of ATP in the presence of ouabain (mg ATPase) and in the absence of ouabain (total ATPase) was determined. Ouabain-suppressible sodium, potassium-dependent ATPase or (Na+ + K+) ATPase was calculated as the difference in the rate of hydrolysis in the presence and absence of ouabain. The activity of the Mg ATPase was significantly reduced in brain after treatment with growth hormone regardless of whether other hormone. In liver there was a significant increase in (Na+ + K+) ATPase in growth hormone, triiodothyronine, or (Na+ + K+) ATPase but there was no effect of triiodothyronine or cortisone and no interaction with the effect of growth hormone. In liver there was a significant increase in (Na+ + K+) ATPase in growth hormone, triiodothyronine, or cortisone-treated animals but Mg ATPase was unaffected by hormone treatment except for the group receiving both growth hormone and cortisone. In kidney homogenates both growth hormone and triiodothyronine significantly increased the activity of the (Na+ + K+) ATPase. There was no effect of cortisone. These data suggest that growth hormone and triiodothyronine may both be calorigenic through their effect on the sodium pumping mechanism in the call membrane.

Ovarian hormones influence brown adipose tissue

Adult female rats were ovariectomized (OVX) or sham-operated and 4-5 weeks later OVX groups were treated with estradiol benzoate (EB), progesterone, both hormones, or the oil vehicle. All rats were sacrificed on the 4th day of hormone treatment following an overnight fast and a terminal meal. Interscapular brown adipose tissue (BAT) pads of EB-treated groups were heavier and contained more lipid than those of the other OVX groups. Lipid content of adipose tissue differed according to site (BAT less than inguinal less than parametrial = retroperitoneal), but only BAT exhibited differential responsiveness to hormonal treatments. There was also a trend for increased oxygen consumption by BAT from EB-treated rats. It is concluded that BAT may be involved in the process of increased energy expenditure by estrogen-treated rats.

Thermogenic capacity and brown fat in rats exercise-trained by running

Brown adipose tissue, a major effector of nonshivering thermogenesis (NST) in mammals, is activated by the sympathetic neurotransmitter norepinephrine. Prolonged increases in norepinephrine levels, whether elicited by cold exposure or exogenous application of catecholamines, lead to increased NST and increased thermogenic capacity of brown fat. Exercise training is also accompanied by enhanced sympathetic activity. The possibility exists that this enhancement may alter brown fat function. The present study was designed to assess the effect of a running exercise regimen on whole animal NST and the in vivo response of brown fat. Rats were trained by running on a treadmill (an average of 17 m/min, 0 degrees incline, for 90 min/d) for a period of at least 6 weeks. Whole animal NST capacity was assessed by monitoring oxygen consumption in response to infusion of norepinephrine. As a measure of the contribution of brown fat to whole body NST, the mass and norepinephrine-stimulated blood flow (microsphere technique) to the tissue were measured. None of these variables differed between the exercised (n = 10) and sedentary (n = 10) groups. That is, there were no significant differences between the two groups with respect to resting oxygen consumption, norepinephrine-induced oxygen consumption, brown fat mass, and brown fat blood flow--whether expressed per gram of tissue or as total tissue blood flow (ie, tissue mass X blood flow per gram). Further study is needed to explain the differential responses of brown fat to the increased sympathetic activity occurring during exercise v that occurring during cold exposure.

Inverse relationship between brown fat thermogenesis and meal size: The thermostatic control of food intake revisited

This study examines a new hypothesis whereby heat production from brown fat in response to eating may serve as a feedback signal for satiety. To test this hypothesis, in vitro respiration rate of brown adipose tissue (BAT) was determined in relation to the voluntary caloric intake of the preceding test meal. This relationship was examined as a function of meal composition and of obesity. It was found that in rats fed a high fat diet, as well as in two types of obese rats (VMH and Zucker), respiration rate per 100 mg tissue was significantly reduced, and energy intake of the preceding test meal increased compared to rats receiving a low fat diet or to respective lean rats. These data lend support to a brown fat mediated thermostatic hypothesis for the control of food intake.

Compositional and Metabolic Changes in Brown Adipose Tissue Following a Single Test Meal

In rats maintained on a scheduled feeding plan, the hypertrophy of brown adipose tissue (BAT) observed after a low-protein/high-carbohydrate single test meal was accompanied by significant changes in the percentage of all major constituents of the tissue. There was a fall in the percentage of water (P less than 0.01), a rise in the percentage of fat (P less than 0.05), and a rise in the percentage of glycogen (P less than 0.001). The largest absolute changes following a meal were in the fat content, which almost doubled, and in the glycogen content, which exhibited about a four-fold increase. Deposition of fat in the BAT following the test meal was accompanied by a three-fold increase in the rate of fatty acid synthesis (P less than 0.05). The in vitro respiration rate of BAT was usually significantly increased in the meal-fed rats, but the effect of replacing the protein content of the test meal with starch was not clear. A lower protein, higher starch diet (9% of calories from protein, 72% from starch) resulted in a trend for a larger thermic effect than a higher protein, lower starch diet (27% of calories from protein, 54% from starch).

Effects of acarbose on food intake, body weight and fat depots in lean and obese rats

Abstract Effects of dietary acarbose at 0, 5, 15 and 50 mg per 100 g diet on food intake and body weight were studied for two months in female rats. The relationships between diet composition, the drug dose and the type of obesity were examined. In lean rats receiving the drug in a high carbohydrate diet (70 Cal.%), mean food intake was similar to control at 5 and 15 mg dietary levels, but was significantly increased at 50 mg. Body weight was significantly reduced only at the 15 mg level. In VMH obese rats receiving the drug in a high carbohydrate diet, it resulted in significant reductions in food intake at the 15 and 50 mg drug levels and in significant reductions in body weight at all three drug levels. In dietary obese rats receiving the drug in a high carbohydrate diet and also in a 32% sucrose drinking solution, food intake and body weight were significantly reduced at each of the drug levels. In dietary obese rats receiving the drug in a high fat diet (70 Cal.%), acarbose at all levels resulted in only small and usually not significant changes in either food intake or body weight. Weight of fat depots were significantly reduced at the 50 mg dietary level in all instances where a high carbohydrate diet was used while at the 5 mg level, fat depots were reduced only in the VMH obese, with the sucrose obese showing a trend for reduced depots. Acarbose in the high fat diet resulted in no significant changes in weight of fat depots. These data indicate that acarbose in a high carbohydrate diet is effective in reducing weight of rats, and that obese usually show a greater reduction in food intake and body weight than lean rats.

Guanethidine sympathectomy does not prevent meal-induced increases in the weight or oxygen consumption of brown fat

The interscapular brown adipose tissue (BAT) of adult rats that were neonatally sympathectomized with guanethidine (GUA) consumed less oxygen but weighed the same as BAT from intact controls. In response to a 2-hr mixed-constituent meal, BAT from sympathectomized and control rats showed similar increases in oxygen uptake and weight. These data suggest that some functions of BAT can be maintained even without sympathetic stimulation.

Effects of acarbose in rats are influenced by the type of dietary starch

When rats consume a high cornstarch (raw) diet containing the alpha glucosidase inhibitor acarbose, they transport a large portion of the undigested starch into the large bowel, causing massive distention of the lower GI tract. In the present study we compare the effects of acarbose (50 mg per 100 g diet) when mixed in a raw cornstarch diet to its effects when mixed in a cooked cornstarch diet of otherwise identical composition. Controls received the respective diets but without the drug. In contrast to its effects when mixed in the raw cornstarch, mixed in the cooked cornstarch diet, acarbose consumption was not accompanied by any significant fecal losses of dietary starch. The intestinal distention induced by the drug was also much smaller in the rats eating the cooked cornstarch than the raw cornstarch. When either diet contained acarbose, fat depot weights were significantly lower than when the diets did not contain the drug. However, the difference was consistently greater with the raw cornstarch diet.