Induction of Ovulation in Rats by Direct Intrapituitary Infusion of Median Eminence Extracts

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Abstract
The possible existence of a hypothalamic humoral substance(s) capable of releasing the ovulating hormone from the adenohypophysis was studied. “Pentobarbital blocked” proestrous rats were used, and the effect on ovulation of various materials was determined upon direct intrapituitary infusion. The substances tested were acid extracts of bovine and rat median eminence tissues, bovine hypothalamic and cortical tissues, arginine-vasopressin, epinephrine, histamine and extraction solvent. Of 34 animals that received the intrapituitary infusion of bovine and rat median eminence extracts, 24 ovulated following the infusion. When bovine extracts were administered intravenously the effective dose had to be increased 10 to 48 times that infused into the pituitary, in order to elicit a response. Twenty-eight animals were used for the intrapituitary infusions of control substances. Only 1 of these animals ovulated following the infusion. Additional controls comprised 10 animals that received only the blocking injections of pentobarbital, 6 animals in which cannulae were placed into the pituitary in addition to barbiturate injections and 17 animals that received infusions of the various substances but in which the pituitary cannulae were unintentionally misplaced. None of these animals ovulated following the various procedures. These findings suggest that the median eminence of the tuber cinereum contains a substance(s) capable of releasing the ovulating hormone from the rat adenohypophysis.