Plasma oestrogen levels during the canine oestrus cycle.

Peripheral plasma samples were obtained during pro-oestrus and oestrus from two adult Beagle bitches and from one animal (bitch 124) during its first oestrous cycle. The animals were housed in a constant environment kennel and each showed a normal oestrous cycle as judged by clinical appearance, vaginal cytology and behavioural tests; in addition, a rise in plasma progesterone was noted during late oestrus and early metoestrus (Christie, Bell, Horth & Palmer 1971). Plasma oestrogens were measured by the radioimmunoassay technique of Abraham (1969), with modifications. No separation of oestradiol and oestrone was undertaken and the results are thus an estimate of total immunoreactive oestrogens. The water blank for the method was 16 ± 6·5 (S.D.) pg/ml while the solvent blank was 19 ± 4·7 pg/ml. The results were corrected for the solvent blank. The recovery of oestradiol added to water was 102 ± 12 (S.D.)%, and to plasma from a bilaterally ovariectomized, hemi-adrenalectomized^.

Reproductive endocrinology of bitches.

Domestic dogs are mono-oestrous and predominantly non-seasonal breeders with ovarian cyclicity unrelated to uterine function. During the first phase of dioestrus or pregnancy luteal function seems to be independent of gonadotrophic support and the gradual decline of progesterone concentration thereafter occurs in spite of an increased availability of prolactin and luteinising hormone (LH). Thus, the mean area under the curve (AUC) for LH (ng per 360 min ml⁻¹) increased from 1672 in early dioestrus to 2510 in late dioestrus and from 2940 on day 20 to 5089 on day 55 of pregnancy. LH pulse frequency remained unchanged. An induced release of LH during each quarter of dioestrus had no immediate effect on progesterone concentration but production over the whole period of dioestrus was increased (P < 0.03). Results from blocking cyclooxygenase activity indicated that the rather precipitous luteolysis prior to parturition was PgF_2α-mediated. During anoestrus LH pulse frequency did not change. The AUC for LH decreased from late dioestrus to early anoestrus (6332 vs. 3257 ng per 360 min ml⁻¹) and increased from mid to the end of anoestrus (5830 ng per 360 min ml⁻¹). Only during the terminal phase of anoestrus could resumption of ovarian activity be induced by treatment with oestradiol-17β. There was a depression of oestradiol-17β during mid anoestrus while it increased at the end of anoestrus.

The ovarian cycle of the bitch: plasma estrogen, LH and progesterone.

Diurnal variation of serum progesterone, but not relaxin, prolactin, or estradiol-17B in the pregnant bitch.

The concentrations of progesterone (P), relaxin (Rlx), estradiol (E2) and PRL were measured by specific RIAs in serum samples collected twice daily at 8:00 am and 3:00 pm at weekly intervals after mating and until whelping in five Labrador Retriever bitches. From weeks 3 to 6 of pregnancy, P exhibited a conspicuous and statistically significant diurnal pattern (P < 0.05), its serum concentration being approximately twice as high at 8:00 am as at 3:00 pm. A similar but nonsignificant trend was observed weeks 2, 7, and 8, and the overall ratio of the am/pm P concentrations was 2.4 ± 0.28 (P < 0.001). Rlx, E2, and PRL did not show a diurnal pattern at any time during pregnancy.

The glandular sources and regulation of secretion of Rlx were further investigated. Rlx bioactivity was detected in canine placentas and ovaries, providing supportive evidence that these organs may be a dual source of the hormone in canine pregnancy. Injection of ovine PRL in three pseudopregnant bitches significantly increased serum P concentration as compared with seven untreated pseudopregnant controls, but Rlx was not detectable in serum before, during or after PRL treatment.

Biology and endocrinology of ovulation, pregnancy and parturition in the dog.

There is considerable variation among bitches in commonly encountered intervals between cycles (5-12 months), durations of anoestrus (1-8 months), durations of follicular phase pro-oestrus (3-21 days) and periovulatory oestrous behavior (3-21 days), intervals from preovulatory LH surge to oestrus onset (-2 to 5 days), and intervals from fertile mating to parturition (57-68 days). The extent of variation within bitches ranges from slight to great. However, there appears to be very little variation in the intervals from LH surge to ovulation (2 days), to post-ovulatory oocyte maturation (approximately 4 days), to implantation (approximately 18 days), to selected developmental stages of pregnancy, or to parturition (64-66 days). There are no tests diagnostic of early pregnancy. The onset times of persistent pregnancy-specific changes have been estimated, including radio-opaque fetal details (Day 46), elevated blood prolactin values (Day 35), elevated blood relaxin values (Day 25), echogenic heart beats (Day 24) and embryonic vesicles (Day 19), and potentially palpable uterine enlargements (Day 21). As in humans, there is an anaemia of pregnancy involving a 30% reduction in haematocrit and an increased incidence of insulin resistance during the second half of gestation. Ovarian progesterone is required throughout pregnancy. LH and prolactin are luteotrophic in the pregnant bitch as well as during the 2-month luteal phase of the non-pregnant bitch. Parturition follows a luteolysis which occurs during an increase in prostaglandin F-2 alpha that begins 36 h pre partum. Factors regulating the duration of anoestrus are not known but termination of anoestrus is associated with increased pulsatile secretion of LH.

Concentrações séricas de progesterona, 17 b-estradiol e cortisol durante o final do próestro, estro e diestro gestacional em cadelas.

Neste estudo, foram utilizadas 7 cadelas sem raça definida, adultas e hígidas, copuladas com macho hígido, após exame andrológico, para acompanhamento das variações hormonais de progesterona, 17b-estradiol e cortisol a partir do final do próestro, durante o estro e diestro gestacional em fêmeas da espécie canina. As avaliações séricas do cortisol foram iniciadas no período de estro. A citologia vaginal esfoliativa foi utilizada como parâmetro auxiliar para a determinação das fases do ciclo estral, mais especificamente para análise do melhor momento para cópula, através da presença das células superficiais queratinizadas visibilizadas nas lâminas. Os resultados obtidos mostraram concentrações médias de progesterona elevando-se discretamente no final do próestro (de 1,56 para 2,85ng ml^-1), concomitante com o início do declínio dos valores de estradiol no mesmo período (de 20,93 para 18,81pg ml^-1). Durante a gestação pôde-se observar concentrações elevadas de progesterona (36,90ng ml^-1), havendo declínio apenas no terço final (4,10ng ml^-1), quando também pôde ser notada, por um momento, ligeira elevação das concentrações médias de 17b-estradiol (2,46pg ml^-1). O aumento do cortisol sérico foi notado na última semana da gestação havendo, antes disso, alterações significativas (P<0,05) nas concentrações séricas baseadas nos padrões descritos em literatura. No pós-parto imediato a redução do cortisol sérico (6,52ng ml^-1) foi considerada relevante de acordo com as concentrações detectadas na última semana da gestação (22,27ng ml^-1). A progesterona esteve mantida em níveis basais no pós-parto imediato (< 1ng ml^-1).

Endocrinologia reprodutiva e controle da fertilidade da cadela.

O ciclo estral da cadela possui características distintas das de outras espécies. Estabelecer critérios para a identificação dos estádios do ciclo estral na cadela é essencial para se determinar o momento ideal para cobertura natural ou inseminação artificial. Adicionalmente, com o advento de medidas de prevenção ou término da gestação na cadela, ter a precaução de se utilizar métodos contraceptivos no período mais apropriado do ciclo estral é condição sine qua non para diminuição do surgimento de efeitos colaterais como piometra ou tumores da glândula mamária. O conhecimento das características reprodutivas básicas da cadela é imprescindível para o suporte à clínica e às biotecnias reprodutivas, ainda de uso limitado em cadelas.

Endocrinologia da gestação e parto em cadelas

Os mecanismos relacionados ao controle endócrino do período gestacional e parto em cadelas ainda não estão totalmente elucidados. Desta maneira, a presente compilação de trabalhos científicos referentes aos principais eventos durante a gestação e o parto em cadelas tem por escopo a atualização sobre a endocrinologia em tais eventos fisiológicos e a divulgação sumariada dos conhecimentos gerados a partir das pesquisas científicas na área. É de conhecimento comum que a síntese e a secreção da progesterona, originária principalmente do corpo lúteo, são de extrema importância para manutenção e conseqüente progresso da gestação. Ainda, os níveis plasmáticos desse hormônio podem ser utilizados como método para predizer o momento do parto na espécie canina. Adicionalmente, a relaxina é detectada somente em cadelas gestantes, portanto sua detecção pode ser considerada um método de diagnóstico de gestação. Durante a segunda fase da gestação, observa-se liberação pulsátil de prolactina, simultaneamente ao aumento dos níveis de estrógeno. Entretanto, a influência do estrógeno no mecanismo de secreção de prolactina ainda é incerta. Por outro lado, ao final da gestação, evidencia-se queda dos níveis de progesterona e aumento dos níveis séricos de estrógeno, decorrente principalmente da ação do cortisol fetal. Tais eventos, associados à liberação de PGF2α pelo útero, culminam com o início do parto. O aumento das contrações uterinas e a expulsão fetal ocorrem principalmente pela ação da ocitocina. Entretanto, a ação desse hormônio não requer necessariamente o aumento das concentrações plasmáticas, sugerindo haver uma ação autócrina ou parácrina da ocitocina em cadelas. Embora os estudos relacionados à endocrinologia da gestação e do parto em cadelas tenham elucidado diversas interações e padrões hormonais, tais processos ainda não estão totalmente descritos, uma vez que as cadelas apresentam particularidades reprodutivas que as diferem das demais espécies. Neste particular sentido, futuras pesquisas devem ser conduzidas para contribuir com o conhecimento técnico-científico nesta espécie.

Serum androstenedione and testosterone concentrations during pregnancy and nonpregnant cycles in dogs.

Concentrations of testosterone and of androstenedione were determined by radioimmunoassay in serum samples collected every 2-5 days throughout the periovulatory and luteal phases of the ovarian cycles of pregnant and nonpregnant beagle bitches. Testosterone levels were consistently lower than those of androstenedione, reached peaks of 29 +/- 4 ng/dl near the time of the preovulatory luteinizing hormone peak, and were reduced to near the limits of detection (less than or equal to 5-10 ng/dl) throughout the luteal phase. Androstenedione levels reached preovulatory peaks of 73 +/- 13 ng/dl, were 54 +/- 7 ng/ml during early estrus, increased (P less than 0.05) to early luteal phase peaks of 76 +/- 8 ng/dl between Days 6 and 18, and then declined to 41 +/- 5 ng/dl by Day 35-40 in both pregnant (n = 8) and nonpregnant (n = 4) bitches. Subsequent protracted increases in androstenedione occurred in 4 of 8 pregnancies but in none of the nonpregnant bitches. From Days 42 to 64 the differences in mean levels between pregnant (45 +/- 2 ng/ml) and nonpregnant (32 +/- 3 ng/ml) bitches was not significant (P greater than 0.05). At parturition androstenedione levels fell (P less than 0.05) abruptly from 39 +/- 7 to 13 +/- 3 ng/dl. These results suggest that, in the bitch, androstenedione is the major circulating androgen during the follicular and luteal phases and that patterns of androstenedione levels during the luteal phase parallel those reported for progesterone in pregnant and nonpregnant bitches, including maintenance of elevated levels throughout gestation and an abrupt decline at parturition.

Estradiol-17B, progesterone and testosterone plasma concentrations during estrus in the bitch.

Several studies have reported the hormonal changes occurring during the estrous cycle in the bitch. In this species estrus is characterised by a sharp progesterone increase, because of preovulatory luteinization of mature follicles, and a decrease of estrogens. Even if it has been reported that administration of testosterone propionate to ovariectomised bitches can induce sexual receptiveness (Olson et al., 1984), little is known about the role of androgens in the sexual behaviour of the estrous bitch. The aim of this study was to increase the knowledge concerning sexual steroids changes occurring during estrus in the bitch, focusing on changes associated with the beginning and the end of sexual receptiveness, in the purpose of mating management.