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Ontogeny of Pulsatile Secretion of Gonadotropin-Releasing Hormone in the Bull Calf during Infantile and Pubertal Development^*

Department of Animal Sciences, University of Arizona Tucson, Arizona 85721

Address request for reprints to: Mark E. Wise, Department of Animal Sciences, 228 Shantz Building, University of Arizona, Tucson, Arizona 85721.

Abstract

During the infantile period of development in the bull calf (birth to 6 weeks of age), there is a virtual absence of episodic secretion of LH. Transition from infancy to the prepubertal period (6–10 weeks of age) is characterized by the onset of episodic LH release. This study was conducted to characterize the ontogeny of episodic GnRH release during these developmental periods. During the primary experiment, calves at 2, 5, 8, and 12 weeks of age (n = 4/age) were surgically fitted with cannulae for the collection of mixed hypophyseal portal and cavernous sinus blood. Hypophyseal portal and cavernous sinus and jugular blood samples were collected over a 9- to 12-h period at 10 min intervals. No pulses of LH were observed in calves at 2 or 5 weeks of age. At 8 and 12 weeks of age, pulsatile LH release became evident with a mean of 1.0 ± 0.3 and 2.20 ± 0.7 pulses/10 h, respectively. Unlike LH secretion, calves at both 2 and 5 weeks of age released GnRH in a pulsatile manner (3.5 ± 0.2 and 5.0 ± 0.6 pulses/10 h, respectively). The frequency of pulsatile GnRH release increased from 7.9 ± 0.4 pulses/10 h at 8 weeks of age to 8.9 ± 0.7 pulses/10 h at 12 weeks of age. These findings demonstrate the presence of pulsatile secretion of GnRH during the infantile period of development. Furthermore, the postnatal ontogeny of pulsatile LH release in this species is associated with an increase in the frequency of pulsatile GnRH secretion. (Endocrinology 124: 248–256, 1989)

Footnotes

^* A preliminary report of this work was presented at the 20th Annual Meeting of the Society for the Study of Reproduction, Urbana, Illinois. This work was supported in part by NIH Grant HD-22747, USDA Grant 86-CRCR-1-2123, and the Arizona Agricultural Experiment Station.

Received June 30, 1990.

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