The release patterns of luteinizing hormone in the prepubertal verus the mature cycling gilt under continuous infusion of gonadotrophic releasing hormone as a possible indicator of pituitary maturity

An attempt was made in this study to establish an indicator of the maturity of the pituitary and/or hypothalamo-pituitary axis by comparing the luteinizing hormone (LH) release profile under continuous infusion of gonadotrophic releasing hormone (GnRH) in the prepubertal and mature cycling gilt. This was done in an effort to show whether or not an immature pituitary gland could be responsible for failure to maintain pregnancy in the prepubertal gilt when puberty is induced. The experiment consisted of three prepubertal gilts in one group and three cyclic gilts in a second group. GnRH was administered at a dose rate of 2.3 yg/hr given in pulses over six hours, with blood sampling taking place before, during, and after infusion. Plasma LH values were determined with a human LH radioimmunoassay kit which was shown to be able to detect porcine LH with some reliability. Plasma LH values detected by this kit were below those levels found by some workers for the preovulatory LH surge but were within the range of values which have been reported for times other than estrus. The results showed a significant (P <.05) difference in the mean baseline LH values between groups and no significant (P >.05) difference between groups for mean LH response levels during GnRH infusion. There appears to be a greater change from mean baseline to peak LH levels in the prepubertal gilts, but the increase was not significant (P >.05). It was concluded that a single-peaked or monophasic LH release profile vs. a double-peaked or biphasic LH release profile was not evident in the immature and mature gilts respectively as noted in other species. This appears to have been due to an insufficient dose rate of the releasing hormone (GnRH).