Involvement of Beta-Endorphin in Thermoregulation of Rabbits, Oryctolagus Cuniculus
Rezvani-Bidgoli, Amir Hosein
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https://hdl.handle.net/2142/71428
Description
Title
Involvement of Beta-Endorphin in Thermoregulation of Rabbits, Oryctolagus Cuniculus
Author(s)
Rezvani-Bidgoli, Amir Hosein
Issue Date
1983
Department of Study
Physiology and Biophysics
Discipline
Physiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Animal Physiology
Abstract
Certain neuropeptides alter the thermoregulatory responses and behaviors of the animals by affecting the preoptic/anterior hypothalamus (PO/AH). The primary objective of this investigation is to study the effect of beta-endorphin ((beta)-E) on regulation of body temperature.
Male New Zealand White rabbits, Oryctolagus cuniculus, were stereotaxically implanted with a guide tube above the PO/AH for the injection of (beta)-E, naloxone, sodium salicylate, or physiological saline. PO/AH and ear temperature, oxygen consumption, and evaporative heat loss (EHL) were recorded before and after injection of first saline and then (beta)-E, naloxone, or sodium salicylate at ambient temperatures (T(,a)) of 2-31(DEGREES)C. A 5-(mu)g injection of (beta)-E promoted a rapid reduction in ear temperature followed by a prolonged rise in PO/AH (body) temperature (T(,br)). Preinjection with an isovolumetric amount of naloxone, inhibited the thermoregulatory effects of (beta)-E. The (beta)-E- induced rise in body temperature was directly correlated with T(,a). (beta)-E had no effect on oxygen consumption. (beta)-E inhibited EHL at T(,a)'s of 27 and 31 but not at 5(DEGREES)C. The (beta)-E-induced rise in body temperature was not antagonized by preinjection of sodium salicylate.
In another series of experiments, T(,ear) and T(,br) were recorded in control and (beta)-E pretreated rabbits while radiant heat was applied to the dorsal skin. In control the T(,ear) underwent a rapid increase during back heating. Following (beta)-E administration there was a large reduction in responsiveness of T(,ear) to radiant heat. The time to respond to radiant heat for (beta)-E pretreated rabbits was significantly longer than that for control rabbits. The interaction between norepinephrine (NE) and (beta)-E in regulation of body temperature was examined. The data indicate that (beta)-E-hyperthermia and NE-hyperthermia are mediated through separate pathways. The thermal response to a range of doses of (beta)-endorphin produced a linear dose-response curve.
In conclusion, (beta)-E microinjected into the rabbit induces a reduction in passage of temperature information from cutaneous thermal receptors to the PO/AH and the (beta)-E-induced reduction in sensitivity of the vasomotor system to radiant heat may account for the effectiveness of this opioid peptide in promoting hyperthermia in the rabbit. The (beta)-endorphinergic system may have a natural role in thermoregulatory responses during physical and psychological stress.
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