Mohamed K. Yousef

Thyroid hormones and metabolic rate in burros, Equus asinus, and llamas, Lama glama: Effects of environmental temperature

Abstract 1. 1. Rate of oxygen consumption, V 02 , and thyroid hormones secretion rate were measured in burros, Equus asinus and llamas. Lama glama . exposed to heat, cold and dehydration. 2. 2. The llama had a lower V 02 than the burro. Exposure to heat for 3–4 days and to dehydration decreased V 02 in both species. 3. 3. Plasma levels of T 4 and T 3 were higher in the llama than in the burro. However, secretion rates of T 4 and T 3 were similar in both species. The discrepancy between thyroid hormonal plasma levels and secretion rates in llamas and burros were due to differences in the disappearance rate (K) of these hormones. 4. 4. The difference in V O 2 between the two species does not seem to be related to thyroid function.

Time course of oxygen consumption in rats during sudden exposure to high environmental temperature

Abstract Determination of O 2 consumption of three groups of rats (2, 7 to 8 and 16 months old) following sudden exposure to heat (34°C) demonstrated that: a) O 2 consumption increased significantly in the three groups after exposure to 34°C. This increase was sustained for 48 to 72 hr. b) At 48 to 72 hr after exposure, O 2 consumption was returned to normal (28°C values) and continued to decline significantly below the normal values when data were expressed per animal. c) O 2 consumption increased for less than 48 hr in young rats (2 and 7 to 8 months old) and remained elevated for a longer period (72 hr) in the older rats (16 months). This indicated that the young animals acclimate to 34°C temperature earlier than older animals. The findings characterize the metabolic trends in the sequence of the adjustment changes or acclimation of rats exposed to environmental heat. The data presented indicated that temperature and metabolic rate interrelationships depend on time of temperature exposure.

Blood thyroxine degradation rate of cattle as influenced by temperature and feed intake

Thyroxine I131 disappearance rate (K), PBI, and estimated blood thyroxine degradation rate (TD) were used as parameters of the thyroid function. Results were as follows: (a) cold (1°C) caused a higher thyroid activity (P<.01) as compared to 18°C, (b) the minimum thyroid activity was observed at 35°C, (c) adlibitum feeding caused a higher thyroid function in the cold environment (1°C) than the control-fed group; however, no differences were observed in the hot condition (35°C). Discussion of the different parameters of thyroid activity was presented. The TD estimation was considered to be a good index for quantitative evaluation of the thyroid gland. Mechanisms of feed and temperature effect on thyroid activity were discussed.

Time course of thyroxine I131 disappearance rates in cattle during exposure to hot and cold environments

Estimation of the daily thyroxine I131 disappearance rate in cattle following sudden exposures to heat (38°C) and cold (1°C) conditions demonstrated that (a) the time required for thyroid function to decrease from normal values under heat stress was at least 60 hours, (b) the time for increased thyroid activity under cold required about 36 hours, and (c) the readjustment of the thyroid gland from hot and cold to the thermoneutral zone (18°C) required at least 108 hours. These findings indicated that the adjustment of cattle to a stress condition by alteration of thyroid activity is a relatively slow process. This provides the evidence that thyroid function is not involved in the early stages of acclimation, but it has a major role in the compensation stage of acclimation to the new environment.

Corticosterone plasma levels in desert rodents

Abstract 1. 1. Plasma glucocorticoids were measured in six species of desert rodents. The data indicated that the primary glucocorticoid in all desert rodents is corticosterone. 2. 2. Corticosterone plasma levels appeared to be related to ecological distribution of desert rodents. 3. 3. It is suggested that lower corticosterone plasma levels may play an adaptive role in water conservation and lowered metabolic rates of desert rodents.

Plasma thyroxine levels of mammals: Desert and mountain☆

Abstract Plasma thyroxine levels were measured in twelve species of desert mammals ranging in altitude from the desert floor to montane forest regions. Rodent species from the low desert had lower circulating thyroxine levels than those species found at 1800 m elevation. Total thyroxine plasma levels were significantly related to metabolic rate and ecologic distribution. The low T 4 values of species restricted to the desert floor may play a role in adaptation to summer heat and to the scarcity of food and water.

Body Fat Content and Metabolic Rate of Rodents: Desert and Mountain

Summary Fifteen species of rodents representing three families and a wide range of ecologic distribution were used to investigate relationships between body fat and metabolic rates (Vo2). There was no apparent relationship between fat content and Vo2. The correlation between Vo2, body weight, body water and fat free body weight was essentially the same. Ecologic distribution appears to be of more importance than fat content in modification of Vo2.

Effect of hibernation on oxygen consumption and thyroidal I131 release rate mf mesocricetus auratus

Abstract A continuous recording of O2 consumption, CO2 production and RQ of the golden hamster during the hibernation cycle was presented. The O2 consumption decreased from a value of 2679 to a value of 71 ml/kg/hr. The CO2 production decreased from a value of 2295 to a value of 43 ml/kg/hr. The low RQ during deep hibernation indicates that fat is being utilized. The O2 consumption fell sharply to a minimum value within 4 – 6 hours from the start of its decline and the animals were in deep hibernation within 6 – 8 hours of the start of the hibernation process. Arousal from hibernation was characterized by a sharp increase in O2 consumption, CO2 production and RQ and reached a maximum in approximately one hour. After the sharp increase the values declined to near normal within 90 min. Thyroidal I131 release rate was decreased from a K value of 13.8 to a value of 5.03 during deep hibernation. These results on the energy utilization of the hibernating hamster indicate that during hibernation heat production is regulated at a markedly reduced level.

Total body protein turnover rate in rats: Effects of exogenous thyroxine and thyroidectomy☆☆☆

Abstract The effect of thyroxine (T 4 ) administration and thyroidectomy (Thx) on total body protein turnover rate was investigated in rats using the total body gamma activity of Se 75 labeled methionine. The results indicated that the daily injection of 2 ug of L-T 4 per 100 gm body wt significantly increased protein turnover rate. However, the injection of 4 ug of L-T 4 per 100 gm body wt produced no effect. The Thx rats showed a 32% decrease in protein turnover rate. The possible mechanisms in alteration of protein metabolism by absence or excess of T 4 are discussed.