Ovulation in the rabbit following intraventricular and intravenous administration of synthetic Gn-RH.

A comparison was made of the efficacy of intravenously (iv) and intraventricularly administered synthetic Gn-RH in inducing ovulation in conscious and urethane anaesthetized rabbits. Via the iv route of administration, the minimum dose of Gn-RH required to induce ovulation in all animals of the conscious group was 300 ng/kg body weight. This is in contrast to the larger systemic dose (400 ng/kg body weight) of Gn-RH required to achieve the same results in urethane anesthetized but otherwise identically treated rabbits. This suggests that although ovulation is no blocked by an anaesthetic dose of urethane (1.25 g/kg), the ovulatory response is altered in some way by the anaesthetic. When administered intraventricularly, the minimum dose of Gn-RH required to induce ovulation in anaesthetized animals was only 100 ng/kg body weight or 25% of the equivalent systemic dose. Systemically ineffective doses of Gn-RH (less than or equal to 200 ng/kg body weight) also induced ovulation in the anaesthetized group when administered via the third cerebral ventricle. All animals that ovulated did so between 13 and 16 h following Gn-RH administration and the number of ova recovered paralleled the number of ruptured follicles. A graded increase in the number of ova released with dosage of Gn-RH was not observed. In this study, the smaller defective dose requirement for intraventricularly administered decapeptide supports the view that Gn-RH in the CSF circumvents the general circulation and reaches the portal vasculature directly via the median eminence.