BIOLOGY OF GONADOTROPIN-SECRETION IN ADULT AND PREPUBERTAL FEMALE DOGS

Studies in the female domestic dog demonstrate that luteinizing hormon e (LH) and follicle-stimulating hormone (FSH) have secretion patterns that are pulsatile, are inhibited by oestradiol during pro-oestrus and surge to maximal values before ovulation. Studies in ovariectomized b itches suggest that the periovulatory surge is triggered by a preovula tory decline at late pro-oestrus in the oestrogen:progesterone ratio. During the 3-8-month non-seasonal anoestrus, FSH concentrations usuall y are 50-100% of those of the periovulatory peak, whereas LH concentra tions are only 10-20% of peak values. In ovariectomized bitches FSH co ncentrations are often 5-10 times preovulatory peak values, whereas LH concentrations are only the same as, or double, peak values. Increase d LH concentration and pulse frequency are associated with the termina tion of anoestrus. Treatment with gonadotrophin-releasing hormone (GnR H) pulses or infusions of GnRH agonists can induce fertile oestrus in early anoestrous bitches, as can treatment with a dopamine agonist, pr esumably by suppression of prolactin secretion. Between 4 months of ag e and pubertal pro-oestrus at 8-12 months of age, serum concentrations of FSH and LH are similar to those in adult anoestrus, and are suppre ssed during chronic infusion of GnRH agonist. The latter resulted in a reversible inhibition of puberty during 1 year of treatment. Studies in vivo have shown that LH and prolactin are luteotrophic throughout m ost of the luteal phase. LH stimulated progesterone synthesis by bitch luteal cells in vitro in the presence or absence of stimulant factors or steroid precursors present in serum.