In pigs, sex-specific differences in FSH secretion occur. During pubertal development in boars, FSH secretion increases in concert with testicular steroids, albeit the magnitude of change in FSH varied with the study. In contrast, FSH secretion in females decreases during pubertal development. A number of possibilities may account for this gender difference, including a difference in inhibin secretion or sensitivity to inhibin feedback, or a difference in the relative roles of activin and GnRH in regulation of FSH synthesis. In females, GnRH may be the primary regulator rather than activin, or females may be more sensitive to negative feedback regulation of FSH by inhibin and/or steroids. Immunization against GnRH consistently reduced blood FSH concentrations of female pigs, but in boars the response has varied from no effect to inhibition; K.L. Esbenshade, personal communication).
With differential-display PCR, a porcine calmodulin cDNA fragment of 290 bp was observed to be expressed in greater abundance in anterior pituitary RNA from WC than from MS boars (unpublished results). However, in the present study no expression differences were detected between boars classified as having high or low FSH concentrations when calmodulin-specific primers were used to amplify cDNA synthesized from pituitary RNA (Fig. 2). This indicates that the expression difference of the calmodulin gene between MS and WC boars is a breed difference independent of the elevated FSH concentrations detected in MS boars. proventil inhaler
In summary, we demonstrated that expression of the I/ A pB-subunit gene was positively associated with that of the FSHp gene in sexually mature boars, and the association between FSHp mRNA and plasma and pituitary FSH concentrations was also confirmed. In contrast, FSHp gene expression was not associated with FS or GnRH-R mRNAs in these crossbred boars. It remains to be determined why the boars with elevated plasma FSH concentrations are capable of expressing more I/A pB-subunit gene and whether significant differences of activin B can be detected in the pituitaries of boars with high FSH relative to those with low FSH.