Serum Levels of Luteinizing Hormone and Progesterone During the Estrous Cycle, Pseudopregnancy and Pregnancy in the Dog¹²³

Abstract

Serum levels of LH and progesterone were measured by radioimmunoassay and competitive protein binding techniques respectively in nonmated, sterile-mated (to a vasectomized male) and fertile-mated female beagles. There were no differences in the pattern of LH secretion in the non-pregnant and pregnant animals. The levels of LH were elevated for approximately 4 days, with the peak concentration (2 7 ± 5.2 ng/ml) occurring on the day prior to the first day of standing estrus. At all other times, LH remained between 2-4 ng/ml. Ovulation was observed late on the first day of standing estrus or nearly 24 hr after the LH peak. By 10 days after the LH peak, the concentration of progesterone had increased to 20-30 ng/ml in the nonpregnant and pregnant dogs. In all nonpregnant animals, the pattern of progesterone secretion after day 10 was similar: decreasing from day 10 and subsequently waning to nondetectable levels (<0.5 ng/ml) by 80 days after the LH peak. On the other hand, in the pregnant dogs, progesterone levels generally decreased 10-15 days after the LH peak but then increased dramatically to reach maximum levels (47 ± 3.1 ng/ml) 20-25 days after the LH peak. Progesterone concentration then gradually decreased to nondetectable levels by the day following parturition (day 65). These results suggest: a) the formation of functional corpora lutea is not dependent on mating, and they can remain functional beyond the normal time of parturition (80 vs 65 days), b) the patterns of LH and progesterone do not differ in overt pseudopregnant dogs (those that lactate) and covert pseudopregnant dogs (those that don't lactate) and c) some factor, perhaps from the placenta, may stimulate the corpora lutea of pregnancy 15-25 days after the LH peak. (Endocrinology 94: 404, 1974) T HE reproductive cycle of the dog is characterized by the following events: first, the dog has only one estrous cycle during the breeding season, and it is characterized by rather lengthy periods of proestrus and estrus, each lasting from 5-12 days

Oestrogen and progesterone concentrations in peripheral blood in pregnant red foxes (Vulpes vulpes)

“…in the ewe (Bassett, Oxborrow, Smith & Thorburn, 1969), coypu (Rowlands & Heap, 1966) and rat (Wiest, 1970). A similar profile of progesterone secretion during pregnancy is observed in other canids, such as the blue fox (Moller, 1973) and the domestic dog (Parkes, Bell & Christie, 1972;Smith & McDonald, 1974;Hadley, 1975;Graf, 1978). These observations seem to indicate that, in canids, luteotrophic factors originating from the placenta do not influence the corpus luteum function.…”

“…Hadley (1975) also failed to observe the fall in progesterone concentrations after oestrus and subsequent large rise to peak gestational levels 19-24 days after the first day of oestrus which was described by Smith & McDonald (1974). Graf (1978) has confirmed the observations of Smith & McDonald (1974) and suggested an extra-ovarian source of progesterone for the second increase in serum progesterone concentration observed, which coincides with the time of implantatio'n. We have been unable to clarify the question of whether the corpus luteum is the major site of progesterone production in the red fox.…”

“…Laparotomy and ovari¬ ectomy in early pregnancy cause abortion (unpublished). Despite individual differences, pregnant foxes showed only a non-significant decline in peripheral progesterone before parturition, unlike the blue fox (Moller, 1973) and the bitch (Smith & McDonald, 1974;Graf, 1978) Text- fig. 1.…”

“…These observations seem to indicate that, in canids, luteotrophic factors originating from the placenta do not influence the corpus luteum function. Smith & McDonald (1974) suggested that such factors could be present in the bitch but Hadley (1975) denied this possi¬ bility. Hadley (1975) also failed to observe the fall in progesterone concentrations after oestrus and subsequent large rise to peak gestational levels 19-24 days after the first day of oestrus which was described by Smith & McDonald (1974).…”

“…Smith & McDonald (1974) suggested that such factors could be present in the bitch but Hadley (1975) denied this possi¬ bility. Hadley (1975) also failed to observe the fall in progesterone concentrations after oestrus and subsequent large rise to peak gestational levels 19-24 days after the first day of oestrus which was described by Smith & McDonald (1974). Graf (1978) has confirmed the observations of Smith & McDonald (1974) and suggested an extra-ovarian source of progesterone for the second increase in serum progesterone concentration observed, which coincides with the time of implantatio'n.…”