Abstract
Two experiments were conducted to compare amounts of mRNAs for gonadotropin subunits in two breeds of pigs that are genetically distinct with respect to litter size: the Chinese Meishan and the white composite (a composite of four European white breeds: Yorkshire, Landrace, large white, and Chester white). In experiment 1, pituitaries were collected from mature Meishan (n = 5) and white composite (n = 6) boars. In experiment 2, boars were assigned to three groups according to peripheral concentrations of FSH: white composite (approximately 100 ng/ml; n = 8), Meishan with low FSH (< 500 ng/ml; n = 7), and Meishan with high FSH (> 750 ng/ml; n = 7). Within each of the three groups, five males were castrated. Two months after castration, pituitaries were collected from castrates and from eight contemporary boars for comparison purposes. Concentrations of FSH and LH were measured in half of each pituitary by RIA. RNA was isolated from the other half of each pituitary, applied to Northern and slot blots, and hybridized with cDNA probes for bovine alpha, LH beta, or FSH beta subunits. In experiment 1, pituitary concentrations of FSH (micrograms FSH/mg pituitary) were greater (p < 0.05) in Meishan (40 +/- 7 micrograms/mg; mean +/- SE) than in white composite boars (19 +/- 4). Pituitary weight and content of FSH were greater (p < 0.01) in Meishan boars (335.1 +/- 18 mg and 13.5 +/- 18 mg/pituitary, respectively) than in white composite boars (270.9 +/- 12.0 and 5.0 +/- 1.2, respectively). Northern analysis indicated that sizes of gonadotropin subunit mRNAs were similar in pigs and cattle. Amounts of mRNA for alpha subunit and LH beta subunit were not different (p = 0.14 and 0.08, respectively) between breeds. Meishans, however, had greater (p < 0.01) amounts of mRNA for FSH beta subunit than white composites. In experiment 2, amounts of mRNA for alpha, LH beta, and FSH beta subunits were not different (p > 0.05) between castrated and intact animals. Meishan males with high FSH had greater (p < 0.05) amounts of mRNA for all three gonadotropin subunits than did white composite males. From these results we suggest that greater levels of gonadotropins in the circulation of Meishan boars result, in part, from increased amounts of mRNA for gonadotropin subunits as compared with those in the white composite breed of boars.
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