Our results do not support a strong relationship between FSHp and GnRH-R expression levels in boars and agree with earlier findings in female pigs, ewes, and cows that GnRH, at the physiological stages investigated, was not the major regulator of FSH secretion. Even though LH secretion was stimulated by pulsatile administration of GnRH after hypothalamic-pituitary disconnection of pigs and ewes or nutritional restriction of cows, blood FSH concentrations in these same females were not affected by GnRH pulses. Furthermore, passive immunization of ovar-iectomized female pigs against GnRH decreased LH secretion rapidly within 3 h, whereas FSH secretion remained stable for 8 h and then decreased slowly during the next 8 days. From these observations we predict that in boars, regulation of FSH by GnRH occurs at a secondary level and that activin is a primary regulator. Cheap Diskus Advair
From observations obtained with perifusion of pituitary cells from male rats, Besecke et al. determined an activin requirement for GnRH stimulation of FSHp gene expression. Additionally, they proposed that infrequent pulses of GnRH, as occur in males, stimulate FSHp expression without having an effect on FS expression. Present results in boars support this component of their model; however, they also observed that frequent pulses of GnRH stimulated FS expression resulting in decreased FSHp expression via FS inhibition of activin. Such differences in FS expression do not account for the diverse differences in FSHp expression or FSH secretion that we observe in boars (Figs. 1 and 3).