Our previous studies in ovariectomized ewes have provided direct evidence that FSH secretion is comprised of basal and episodic modes. In those studies, each
GnRH pulse coincided with an FSH pulse, but additional FSH pulses were noted. To determine whether non-
GnRH-associated pulses of FSH represent a
GnRH-independent component of FSH secretion, we determined whether episodic FSH secretion persists after blockade of
GnRH action with a
GnRH antagonist. Hypophyseal portal and jugular blood was collected from five ovariectomized and six luteal phase ewes at 5-min intervals for 6 h before and 6 h after a single iv injection of
Nal-Glu (10 micro g/kg
body weight). Hypophyseal portal LH and FSH and jugular patterns of FSH were compared with patterns of
GnRH. Before
Nal-Glu, in both models, there was a one-to-one concordance between
GnRH and portal LH pulses, and each
GnRH pulse was associated with a FSH pulse. However, additional non-
GnRH-associated pulses of FSH were present.
Nal-Glu administration eliminated LH but not FSH pulsatility.
Nal-Glu inhibited interaction of
GnRH I with
GnRH type I receptor but not interaction of
GnRH II with type II receptor. These studies provide the first direct evidence of the existence of an acute
GnRH I-independent component of episodic FSH secretion.