Negative Feedback Control of Luteinizing Hormone Secretion in Prepubertal Beef Heifers at 60 and 200 Days of Age

Publisher Website
Google Scholar
Abstract
Prepubertal beef heifers at 60 and 200 d of age, born in the fall or spring, were assigned randomly to one of three treatment groups: (1) intact = I; (2) bilateral ovariectomy (OVX); or (3) OVX plus estradiol-17β(E2) administered in silastic implants (OVX + E2). Luteinizing hormone (LH) was measured in serum samples collected at 20-min intervals for 4 h from heifers on —1, +7, +21, +35 and +49 d after OVX. Luteinizing hormone concentrations increased in the serum by 7 d after OVX in heifers at both 60 and 200 d of age (P<.001; time x treatment). Prior to OVX, the LH patterns were characterized by low levels and infrequent episodic pulses. By 49 d after OVX, the mean LH concentrations increased and the pattern changed to one of rhythmic LH pulses with a periodicity of 1 h (P<.001; time X treatment). Estradiol-treated OVX heifers did not exhibit a postovariectomy rise in serum LH concentrations. Serum E2 concentration 49 d after OVX in OVX heifers was threefold greater than in I or OVX heifers, thus demonstrating that E2 exerted negative feedback on pituitary LH secretion in prepubertal heifers. There was no measurable difference in serum E2 concentrations between I and OVX heifers; however, the contrast in the concentration and pattern of serum LH between the two groups was dramatic and suggested gonadal factors in addition to E2 are involved in controlling LH secretion. A negative feedback system of ovarian origin plays a role in controlling LH secretion by 60 d of age, but there was no age-related change in the sensitivity of the - hypothalamic-pituitary axis to negative feedback exerted by E2 in these prepubertal heifers. Copyright © 1984. American Society of Animal Science . Copyright 1984 by American Society of Animal Science.

This publication has 2 references indexed in Scilit: