Effect of anaesthetics on PRL and LH secretion in rats. Importance of pre-anaesthetic adaptation and involvement of monoaminergic neurons.

General anaesthesia has been reported to interact with neuroendocrine functions leading to large variations in basal and stimulated plasma levels of several hormones, but the findings are often contradictory. In the present investigation we have attempted to clarify the importance of the experimental procedure when evaluating the influence of anaesthetics on the secretion of PRL and LH in male rats. One group of rats (non-adapted) were anaesthetized (ip) with pentobarbital (P), urethane (U), ketamine (A), or althesin (A) without being accustomed to the laboratory environment prior to anaesthesia. Another group of rats (adapted) were kept for 90 min in their individual cages before induction of anaesthesia with P or U. In non-adapted rats the plasma concentration of PRL declined rapidly during the first 30 min following administration of all anaesthetics or saline (controls) and attained a steady level after 60 min. Except for a brief rise following U injection, the LH concentration was not affected by anaesthesia in the non-adapted rats. In adapted rats, the concentration of both PRL and LH declined markedly during the pre-anaesthetic adaptation period and had stabilized at the end of that period. Following administration of U, P or saline, no further changes in the hormone concentrations were observed. Injection of the dopamine receptor antagonist pimozide prevented the decrease in plasma PRL during the adaptation period, but had no effect on LH secretion. In pimozide-treated rats, U caused a 5-fold increase in the PRL concentration. This effect of U was inhibited by the serotonin receptor antagonist methysergide. The PRL response to 30 micrograms of histamine was similar in conscious and U-anaesthetized rats, whereas P anaesthesia caused a reduction in the response.(ABSTRACT TRUNCATED AT 250 WORDS)