Thermoregulatory (core, surface and metabolic) responses of unrestrained rats to repeated POAH injections of β-endorphin or adrenocorticotropin
1984; Elsevier BV; Volume: 5; Issue: 4 Linguagem: Inglês
10.1016/0196-9781(84)90012-3
ISSN1873-5169
Autores Tópico(s)Biochemical effects in animals
ResumoRepeated preoptic-anterior hypothalamic (POAH) injections of saline and 10 or 25 μg/μl of β-endorphin or ACTH were given to groups of male Sprague-Dawley rats. One hr after the fifth injection of β-endorphin or ACTH, each rat received a POAH injection of naloxone HCl (10 μg/μl). Core (Tre-rectal) and surface (Tt-tail) temperatures, metabolic (VO2) and behavioral responses were recorded 30 min before and 60 min after each drug injection. The initial POAH injection of either dose of β-endorphin produced a hyperthermia. Peak hyperthermia was reduced in the group given 10 μg/μl of β-endorphin repeatedly. Tts rose after each β-endorphin injection but temporally lagged Tre increases. Metabolic rate (VO2) was increased with repeated POAH injections of β-endorphin. Naloxone reduced the elevated Tre seen with β-endorphin by increasing Tt's further and reducing VO2. POAH administration of ACTH evoked only a slight hyperthermic Tre response, but elevated Tts and VO2s, due to enhanced grooming and explorative behavior. With repeated ACTH injections, Tres did not change from those on the first day as Tts and VO2 remained enhanced. Naloxone reduced VO2 and Tts of the ACTH-treated rats but Tres still were unchanged. Results suggest that the hyperthermia of unrestrained rats given an acute as opposed to repeated POAH β-endorphin injections is mediated by different effector mechanisms. With the doses used, the slight and unchanging Tres seen with ACTH occurred because this peptide increased heat production due to locomotor activation yet also exaggerated heat loss by vasodilating the peripheral vasculature.
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