Related Experiment Videos
Diminished metabolic responsiveness to beta-adrenergic stimulation in estradiol benzoate-treated rats
1Department of Physiology, University of Florida, College of Medicine, Gainesville.
Abstract:
Earlier studies have shown that chronic treatment with estradiol benzoate reduced the responsiveness of heart rate, drinking, and tail-skin temperature to administration of the beta-adrenergic agonist, isoproterenol. The objective of the present study was to assess the relationship between the isoproterenol-induced elevations in rate of oxygen consumption and tail-skin temperature in adult ovariectomized rats treated chronically with estradiol benzoate (28 micrograms/day) and untreated, ovariectomized controls. Isoproterenol (0, 10, 25, and 50 micrograms/kg, s.c.) elevated both rate of oxygen consumption and tail-skin temperature in ovariectomized and ovariectomized plus estradiol benzoate-treated rats in a dose-related fashion. However, in both cases the response of the estradiol-treated group was less than that of controls. A comparison of the regressions of rate of oxygen consumption versus dose of isoproterenol administered to each group revealed significant differences between the intercepts, but not the slopes. A similar comparison with respect to the regression of tail-skin temperature versus dose of isoproterenol administered to each group revealed significant differences between both the slopes and intercepts of the relationships. A comparison of the regressions of rate of oxygen consumption versus tail-skin temperature for control and estrogen-treated rats revealed significant differences between both slopes and intercepts of the relationships. The latter comparison suggests a reduced change in tail-skin temperature for a given change in rate of oxygen consumption in the estrogen-treated group. It is concluded from these results that the reduction in metabolic response to beta-adrenergic stimulation in estrogen-treated rats explains, in part at least, the attenuated response of tail-skin temperature. The tail of the rat is important in short-term temperature regulation. When threatened acutely with overheating, the rat uses its tail as a heat radiator, increasing its skin blood flow, temperature, and heat loss. Administration of isoproterenol to rats at doses of 50-100 micrograms/kg, subcutaneously can increase tail-skin temperature as much as 6 degrees C. This response is mediated by beta-adrenoceptors since it can be either attenuated or prevented by prior administration of propranolol. It serves as a simple and reliable test of beta-adrenergic responsiveness in rats. Chronic treatment with the oral contraceptive, Enovid (7.5 mg/kg food) attenuated this response. Chronic administration of the estrogenic component (ethinyl estradiol, 48-50 micrograms/kg/day) of Enovid also attenuated the response.(ABSTRACT TRUNCATED AT 400 WORDS)
Insights
Chronic estradiol benzoate treatment in ovariectomized rats reduces metabolic and tail-skin temperature responses to isoproterenol, indicating estrogen
Area of Science:
- Endocrinology
- Physiology
- Pharmacology
Background:
- Chronic estradiol benzoate treatment is known to reduce responsiveness to beta-adrenergic agonists like isoproterenol.
- The tail's role in thermoregulation and its temperature response to isoproterenol are established.
- Estradiol's impact on metabolic rate and tail-skin temperature regulation requires further elucidation.
Purpose of the Study:
- To investigate the relationship between isoproterenol-induced oxygen consumption and tail-skin temperature in estradiol-treated rats.
- To compare the dose-response of oxygen consumption and tail-skin temperature to isoproterenol in ovariectomized rats with and without estradiol benzoate treatment.
Main Methods:
- Adult ovariectomized rats were treated with estradiol benzoate (28 µg/day) or left untreated.
- Isoproterenol was administered subcutaneously at doses of 0, 10, 25, and 50 µg/kg.
- Oxygen consumption and tail-skin temperature were measured, and regression analyses were performed.
Main Results:
- Isoproterenol increased oxygen consumption and tail-skin temperature in both groups in a dose-dependent manner.
- Estradiol benzoate treatment significantly attenuated the responses of both oxygen consumption and tail-skin temperature compared to controls.
- Regression analysis revealed significant differences in slopes and intercepts for tail-skin temperature vs. isoproterenol dose, and for oxygen consumption vs. tail-skin temperature.
Conclusions:
- Reduced metabolic response to beta-adrenergic stimulation in estrogen-treated rats contributes to the attenuated tail-skin temperature response.
- Estrogen treatment alters the relationship between metabolic rate and tail-skin temperature regulation.
- These findings highlight estrogen's role in modulating beta-adrenergic-mediated physiological responses.