Involvement of adrenergic receptor mechanisms within hypothalamus in the fever induced by amphetamine and thyrotropin-releasing hormone in the rat

Abstract

The mechanisms underlying the thermal effects induced by intrahypothalamic administration of either d-amphetamine or thyrotropin-releasing hormone (TRH) has been investigated in conscious rats. Direct administration of d-amphetamine (1–10μg in 1μl) or TRH (1–4μg in 1μl) into the preoptic anterior hypothalamus caused hyperthermia or fever at the ambient temperature (T_a∶ 8, 22 and 30 °C) studied. The fever induced by d-amphetamine or TRH was due to increased metabolic heat production at T_a 8 °C, while at T_a 30 °C the fever was due to cutaneous vasoconstriction in the rat. At T_a 22 °C, the fever was due to both increased metabolism and cutaneous vasoconstriction. Furthermore, the fever induced by intrahypothalamic administration of TRH was greatly reduced by pretreatment with intrahypothalamic administration of either yohimbine (a blocking agent of alpha-adrenergic receptors), phentolamine (a blocking agent of alpha-adrenergic receptors) or DL-propranolol (a blocking agent of beta-adrenergic receptors) in the rat. However, the fever induced by d-amphetamine was antagonized by pretreatment with yohimbine or phentolamine, but not with DL-propranolol in the rat. These observations indicate that the adrenergic receptor mechanisms within the hypothalamus are involved in the fever induced by both d-amphetamine and TRH.