Role of 5-HT[7] receptors on lordosis behaviour and LH release in the female rats

ABSTRACT

The present study was designed to investigate the role of the 5-HT [7] receptors in lordosis and release of LH and compare the lordotic responses with 5-HT [IA] agent. Ovariectomised but oestradiol benzoate [OB] [10 micro g] for 48 h plus by progesterone [0.5 mg]- primed receptive rats were used for the study. Thirty min. prior to progesterone 5-HT [IA] and 5- HT [7] agonists were administered intra-peritoneally [i.p.]. Lordotic quotient and release of LH were measured. Agonistic effect was then antagonized by respective antagonists. Effects on the above parameters were noted and correlated for possible interplay. 5-HT [7] agonist mimicked inhibitory effect of 8-OH DPAT on lordosis in receptive rats, however, the response was generally attenuated. Treatment by 5-HT [IA] antagonist, WAY 100135 causing a protective effect was evident transiently. Attenuation of lordotic quotient was again evident in rats treated with 5-HT [7] antagonist. 5-HT and the 5-HT [IA/7] receptor agonist, 8-OH-DPAT, injected i.p. into the female rat inhibit the LH release and the effects of both are blocked by 5-HT [IA] antagonist, WAY 100135 and 5-HT [7] antagonist, SB 269970-A as both 5-HT [IA] agonist, 8-OH-DPAT and 5-HT [7] agonist, 5-CT have moderate activity at the 5-HT [7] receptor subtype, indicating the possibility that this subtype might mediate these effects has been investigated. Ovariectomised but steroids primed rats induces an LH surge. [5-CT], a potent but non-selective agonist at 5-HT [7] receptors, like 5-HT and 8-OH-DPAT inhibited the LH surge at 2 mg injected i.p. The selective 5-HT [7] receptor antagonist SB-269970-A blocked LH surge when given systemically at both 5-HT [IA] and 5-HT [7] receptor subtypes. These data indicate that 5-HT [7] receptors play a role in the regulation of lordosis and release of LH and there exist a direct correlation between the two