Abstract
Chronic supraphysiological blood levels of growth hormone (GH) may retard sexual maturation in swine. Pigs used in this study included four founder transgenic pigs (two gilts and two boars) expressing a mouse transferrin (TF) promoter fused to a bovine (b) GH structural gene, 13 second- or third- generation transgenic pigs (seven gilts and six boars) expressing a mouse metallothionein (MT) promoter fused to a bGH structural gene and 16 control littermates (eight gilts and eight boars). Blood plasma levels of LH, FSH, estrone and testosterone were measured to determine whether expression of bGH genes altered secretion of hormones between 80 and 180 days of age. Presence of a bGH gene was detected by hybridization of DNA in dot blots of tail biopsies. Expression of a bGH gene was detected by radioimmunoassay of plasma bGH. In four TFbGH founder transgenic pigs bGH ranged from 164 to 1948 ng/ml; in one MTbGH transgenic boar of line 3104 bGH was 1211 ng/ml; and in 12 pigs of line 3706 bGH ranged from 25 to 190 ng/ml. Expression of bGH in transgenic pigs lowered (P=.0192) plasma LH with no significant differences between sexes, had no significant effect on plasma FSH and lowered plasma estrone (P=.0001) and testosterone (P=.0269) in boars (but not gilts). Plasma estrone and testosterone were higher (P=.0001) in boars than in gilts. Plasma FSH was higher (P=.0001) in gilts than boars and decreased (P=.0001) with advancing age in gilts but not in boars. Results indicate that anovulation and decreased libido in transgenic gilts and boars may be related to decreased secretion of LH during sexual maturation.
Published Version
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