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^.

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.

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).

Sexual behavior in ovariectomized bitches in response to estrogen and progesterone treatments.

Sex behavior was quantitated in 13 groups of 2-5 ovariectomized bitches receiving various estrogen and progesterone treatments. In addition, one of the scoring systems used to quantitate sex behavior was applied to the changes observed during proestrus and estrus in 7 intact cycling bitches for which daily serum progesterone and LH levels were assayed. In 6 of the 7 bitches, the onset of full sexual receptivity characteristic of estrus occurred 0-2 (1.2 ± 0.5) days after the LH peak and only after a detectable increase in serum progesterone levels.

Ovariectomized bitches administered estradiol-17β s.c. in 4.7 mm (o.d.) Silastic capsules, at a dose of 0.6 cm/kg for 30 days, became increasingly attractive to males and in some instances showed the passive behavior characteristic of late proestrus. However, none showed the positive reflexes associated with the full sexual receptivity characteristic of estrus. When bitches were administered progesterone implants (1.8 cm/kg) after 8 days of estradiol treatment they displayed within the next 1-5 days a full estrous behavior which lasted for about 1 week. When the estradiol dose was reduced from 0.6 to 0.1 cm/kg at the time of progesterone treatment, each of the bitches showed full sexual receptivity within the next 18 h and this behavior was maintained for 5 days.

Other groups of ovariectomized bitches were injected initially with an estradiol benzoate (EB) dose of 0.4 µg/kg and every 8 h thereafter with steadily increasing doses in increments of 0.2µ g/kg for 3, 6 or 9 days. After 3 days of EB treatment, proestrous but not estrous behavior was observed regardless of whether progesterone was administered after the EB treatment. EB treatment for 6 days caused some bitches to show proestrous behavior prior to termination of treatment and to display estrous behavior following the last EB injection. When 6 days of EB were followed in 8-32 h by progesterone implants (1.6 cm/kg), estrous behavior was observed within 8 h and lasted for 8 days. Estrus occurred earlier and lasted longer in these bitches than in those receiving no additional treatment or small estradiol implants instead of progesterone. Of 9 bitches receiving EB injections for 9 days, 3 showed estrous behavior 1-2 days prior to the last injection while the other 6 displayed estrus only after the last EB injection was given. In each bitch, including those displaying estrous behavior prior to the termination of EB treatment, serum estradiol levels immediately prior to the onset of estrus were lower than those present 12 h earlier. In bitches administered progesterone implants (3.2 cm/kg) 6 h after 9 days of EB treatment, the mean duration of estrous behavior was 9 days vs the 5 days in bitches not subsequently administered progesterone. When progesterone was administered 3 days prior to the end of EB treatment, 1 of 3 bitches showed estrus 8 h following progesterone while the others did not display estrus until after the last EB injection.

These results are considered consistent with the hypothesis that behavioral estrus in the bitch is potentiated by exposure to elevated levels of estrogen and subsequently initiated by a decrease in the estrogen:progesterone ratio effected by either a fall in estrogen and/or a rise in progesterone.

Relationship of serum estrone, estradiol-17b and progesterone to LH, sexual behavior and time of ovulation in the bitch.

Serum estrone, estradiol-17β and progesterone were measured in bitches in which LH, sexual behavior and laparoscopically confirmed time of ovulation had been previously studied. Steroid values from 25 estrous periods were normalized to day of peak LH (Day 0). Estrone, estradiol-17β and progesterone concentration did not differ significantly in either dogs subjected to laparoscopy at 48 h intervals or those bitches undergoing no laparoscopy.

During the preovulatory interval, mean peripheral estrone concentrations were more variable than estradiol-17β; however, both estrogens tended to rise gradually throughout this time period. Overall maximal estradiol-17β concentration was detected on Day -2 with estrone peaking later (Day -0.5). Both estrogens declined (P<0.05) coincidentally with the LH surge. Progesterone from Days -14.0 through -1.5 was maintained at basal concentrations. An increase (P<0.05) in mean progesterone occurred on the day of the preovulatory LH peak which correlated with direct observation of apparent preovulatory follicle luteinization. Progesterone increased gradually from Day -0.5 through 8 and then varied for the remainder of the sampling period.

Analysis of individual cycles indicated that circulating serum concentrations of reproductive steroids fluctuated from day to day or within days of the proestrous-estrous interval. In dogs subjected to laparoscopy, initial evidence of the presence of visible preovulatory follicles was closely related to the first detectable elevations in both estrone and estradiol-17β. Either estrone or estradiol-17β concentrations or both surged sharply in 24 of the 25 cycles examined; however, only titers of estradiol-17β were elevated above baseline in all cycles prior to, or at the time of, the LH peak. In 16 of 25 cycles, estradiol-17β concentrations declined by 20 pg/ml or more 12-24 h prior to the onset of sexual receptivity. Bitches remained in estrus during periods of declining estrone and estradiol-17β and increasing progesterone levels.

These data integrate the hormonal, ovarian and behavioral events of the estrous cycle of the bitch and suggest that: 1) a preovulatory estradiol-17β surge exists and is likely responsible for triggering LH release; 2) estrone may play a supportive role to estradiol-17β in the endocrine control of LH secretion; 3) preovulatory changes in follicular morphology are distinct and can be correlated with a shift from estrone and estradiol-17β to progesterone secretion; 4) prolonged sexual receptivity in this species is supported in the presence of declining estrogen and continuously rising progesterone concentrations.

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.