EXPRESSION OF A BOVINE GROWTH-HORMONE TRANSGENE INHIBITS PREGNANT MARES SERUM GONADOTROPIN-INDUCED FOLLICLE MATURATION IN PREPUBERAL GILTS

Prepuberal gilts were injected with PMSG to determine whether expressi on of a bovine growth hormone (bGH) transgene inhibited preovulatory m aturation of ovarian follicles. Seven transgenic (TG) gilts of line 37 06, which expresses a mouse metallothionein-bGH transgene, and eight n ontransgenic, control (C) gilts (128 to 147 d old) were injected with PMSG, 12.5 IU/kg BW, 72 h before necropsy. Surface ovarian follicles g reater-than-or-equal-to 1 mm in diameter were counted, measured for di ameter, and aspirated for fluid. Follicles were classified morphologic ally as healthy or atretic and those with follicular fluid estradiol-1 7beta greater-than-or-equal-to 100 ng/mL were classified as estrogenac tive (EA). The number of follicles per gilt was 64.3 +/- 6.1 (mean +/- SEM) and did not differ significantly between bGH-TG and C gilts. The PMSG treatment induced growth of large (> 5 mm) follicles in both bGH -TG and C gilts. However, compared with C gilts, bGH-TG gilts had fewe r ( P < .0 5) large follicles (5.9 +/- 1.5 vs 18.3 +/- 5.4), a lower p roportion of EA large follicles (35 +/- 12.5 vs 69 +/- 13.2%), and in large follicles less (P < .05) estradiol-17beta (86 +/- 17 vs 350 +/- 69 ng/mL) and androstenedione (300 +/- 33 vs 1,283 +/- 221 ng/mL). Fol licular fluid progesterone and inhibin did not differ significantly be tween bGH-TG and C gilts. The incidence of atresia among small and med ium follicles did not differ significantly between bGH-TG and C gilts. These results indicate that chronic, unregulated expression of a bGH transgene in prepuberal gilts inhibited follicle growth in response to administration of PMSG and may have blocked estradiol-17beta producti on in vivo by inhibiting theca interna androgen production.