Role of changes in the pulsatile secretion pattern of FSH in initiation of ovarian folliculogenesis in bitches.
The results of two studies in which the pulsatile secretion patterns of LH and FSH were investigated in six Beagle bitches during early, mid- and late anoestrus and in six anoestrous Beagle bitches treated with bromocriptine are summarized to improve our knowledge of the endocrine changes that lead to a new follicular phase in bitches. Blood samples for the determination of secretory profiles were obtained via jugular venepuncture at 10 min intervals for 6 h. In untreated bitches, blood samples were collected during early, mid- and late anoestrus. In bromocriptine-treated bitches (20 micrograms kg-1 twice each day, starting 100 days after ovulation until the start of the next oestrous cycle), blood samples were collected before treatment and at 2 week intervals after the start of bromocriptine treatment until the next ovulation. In all bitches, FSH and LH were secreted in a pulsatile manner and FSH pulses coincided with LH pulses. Progression from early to late anoestrus was associated with an increase in FSH secretion without a concomitant increase in LH secretion. The bromocriptine-induced shortening of the interoestrous interval was also associated with an increase in FSH secretion without a concomitant increase in LH secretion. These results indicate that in bitches an increase in circulating FSH should be considered to be a critical event required for the initiation of ovarian folliculogenesis and consequently the termination of anoestrus.
Kooistra
H S
HS
Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 8, PO Box 80 154, NL-3508 TD Utrecht, The Netherlands.
Okkens
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AC
D000780:Anestrus / Q000502:physiology*; D000818:Animals; D001971:Bromocriptine / Q000494:pharmacology; D004285:Dogs / Q000502:physiology*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood / Q000378:metabolism*; D006727:Hormone Antagonists / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism; D006080:Ovarian Follicle / Q000187:drug effects / Q000502:physiology*; D012636:Secretory Rate / Q000502:physiology
D006727:Hormone Antagonists; D001971:Bromocriptine; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone