Research challenges in endocrine aspects of canine ovarian cycles.

Significant deficiencies exist in understanding factors controlling the nature and timing of critical endocrine changes in canine ovarian cycles. The following merit further study: changes in steroid clearance and binding; mathematically modelling periovulatory hormone rate of change interactions; luteal gonadotropin dependence; endogenous circannual cycles underlying the ovarian cycle; importance of periovulatory follicular steroid dynamics on granulosa and oocytes; in vitro capacity of anoestrous ovarian tissue to demonstrate roles of individual gonadotropins and steroid precursors to increase oestradiol production; factors affecting secretion and activation of the canine female sex pheromone.

Ovulation compensatory function after unilateral ovariectomy in dogs.

As a step towards elucidation of the timing and mechanism of the determination of the number of ovulated ova in dogs, we excised one ovary 2, 5 and 8 days after the beginning of vulval bleeding and examined whether the lost ovulation function, assessed by estimating the number of ovulated oocytes, would be compensated for by the remaining ovary. The number of ovulated ova was maintained by the remaining ovary in the group that underwent unilateral ovariectomy 2 days after the beginning of vulval bleeding. However, in the groups ovariectomized 5 or 8 days after the beginning of vulval bleeding, no compensation for the number of ova that would have been ovulated from the lost ovary was observed; ova were ovulated only from the follicles 3 mm or greater in diameter observed in the remaining ovary at unilateral ovariectomy. Thus, in dogs, the number of ovulated ova is considered to be determined within 5 days after the beginning of vulval bleeding.

Ovulation day after onset of vulval bleeding in a beagle colony.

This study investigated the duration of the interval between the onset of vulval bleeding at pro-oestrus and ovulation estimated from the plasma progesterone concentration in a large number of beagle bitches. The influence and association of individual variation, ageing and duration of the oestrous cycle were also investigated. The mean time of ovulation after the onset of vulval bleeding was 11.1 ± 0.2 days, but it widely ranged from 3 to 31 days. This timing was not influenced by age or duration of the oestrous cycle, and within-individual variation was small. As there has been no previous report in which the ovulation day was investigated by the age, these data may be very valuable.

Endocrinologic control of normal canine ovarian function.

In dogs, the termination of the 3-10-month obligate anoestrus involves selection of a cohort of LH-sensitive follicles, presumably from a wave of dominant small antral follicles that would otherwise undergo atresia. The number and size of such follicles appears to increase, especially during the last 50 days of anoestrus when the already elevated concentrations of FSH become further elevated. The final selection and eventual terminal development of these follicles is caused by an increased frequency of high-amplitude LH pulses at the end of anoestrus. Concomitant increases in FSH are typically small or negligible. High concentrations of FSH in anoestrus are likely to be important in maintaining, if not stimulating, overlapping waves of dominant follicles throughout anoestrus, their expression of aromatase activity and basal oestradiol secretion sufficient to suppress LH by negative feedback. An attractive hypothesis is that late anoestrus increases in LH-stimulate synthesis of precursor androgen for already available FSH-dependent aromatase. After 7 or more days of elevated LH, and perhaps 2-5 days of semi-autonomous growth, with maximal oestradiol production reached, follicle capacity to further increase oestradiol becomes limited and excess progesterone becomes increasingly secreted. The pre-ovulatory LH surge and oestrus onset are then triggered - often synchronously and in concert with the terminal maturation of the follicles - by central effects of the large decrease in the oestrogen to progestin ratio. Follicular endocrine and paracrine events during and following the LH surge are likely similar to those reported for other species. The prolonged luteal phase lengths of 55-75 days in non-pregnant bitches bracket the 64 +/- 1 day in pregnancy and represent a genetically programmed luteal cell lifespan approximating gestation length as occurs in the luteal phase of hysterectomized animals of most polyoestrous artiodactyls and rodents. The 30-40-day slow regression after day 20 to 30 involves periodic cell death, diminution in cell size, low levels of apoptosis and minimal or modest involvement of endogenous prostaglandin F (PGF) production. The canine corpus luteum (CL) is dependent on both LH and prolactin as stimulating luteotrophins by day 15, and as required luteotrophins by days 20-25, if not earlier. Thereafter, both luteotrophins likely have cellular mechanisms of action similar to those reported for other species. Progesterone secretion during pregnancy is greatly enhanced by characteristic, and probably relaxin-stimulated, increases in prolactin concentration starting at or after day 25, and persisting to term. Near term, foetoplacental maturation results in the placental release of large, luteolytic amounts of PGF for 1-2 days pre-partum. Pre-partum luteolysis, like that induced by exogenous prostaglandin, likely involves a cascade enhanced by the removal of progesterone inhibition of PGF release and some degree of intra-luteal PGF synthesis. That a likely twofold or greater increase in progesterone production by the CL of pregnancy does not result in significantly higher serum progesterone than in non-pregnant metoestrus relates to several biological changes, including a large increase in plasma volume of distribution, increased metabolism of progesterone by increased uterine, placental and mammary masses and increased liver clearance and excretion of progesterone and progesterone metabolite. Anoestrus length and ovarian cycle intervals, variable within and among bitches, are likely affected by neuroendocrine components of an endogenous circannual cycle, albeit only photo-entrained in the Basenji breed. This may be modified by the prior luteal phase, exposure to oestrus female pheromones and as yet unknown mechanisms that likely operate via inhibitory opioidergic and/or stimulatory dopaminergic hypothalamic pathways affecting late anoestrus increases in LH.

Prolonged duration of fertility of dog ova.

The fertile period for natural mating in dogs extends from before ovulation until day 5 post ovulation (PO) and involves a delay in oocyte maturation until 2-3 days PO and viability of secondary oocytes for 48-60 h or more. Spermatozoa do not enter the uterus after vaginal insemination in late oestrus. Cervical closure appears to occur on average 5 days PO, but conception may occur following intrauterine artificial insemination (IUAI) up to 8 days PO. Therefore, the present study was conducted to clarify the duration of fertility of canine ova. Using IUAI at 6, 7, 8 and 9 days PO (n = 5 bitches each) conception rates were 100%, 71.4%, 37.5% and 0%, respectively, with an average litter resorption rate of 30.8%, and with mean litter sizes and times to delivery PO being 4.3 +/- 1.6 and 64.3 +/- 0.3 days, 4.0 +/- 1.4 and 66.3 +/- 0.4 days, and 2.5 and 68 days for IUAI at 6, 7 and 8 days, respectively. The high pregnancy rates with IUAI at 6 and 7 days PO confirm that many canine oocytes are fertile at 4-5 days after maturation. The high rate of resorption was presumably because of aging of ova or asynchrony between embryonic development and the intrauterine environment.

Plasma progesterone and prolactin concentrations in overtly pseudopregnant bitches: a clinical study.

Plasma concentrations of progesterone (P(4)) and prolactin (PRL) were measured in 35 bitches presented at veterinary clinics for symptoms of overt pseudopregnancy (PSP) between 50 and 95 days after the onset of proestrus. Results were compared to those from samples collected from 35 control bitches at comparable stages of the ovarian cycle (expressed as days after the onset of observed signs of proestrus). In the PSP bitches at 71.4+/-1.6 (mean+/-S.E.M.) days of the cycle, P(4) (1.5+/-0.2ng/mL) was lower (P<0.01) and PRL (16.0+/-1.9ng/mL) was higher (P<0.01), compared to P(4) (2.7+/-0.4ng/mL) and PRL (2.9+/-0.6ng/mL) in control bitches at 70.6+/-1.5 days of the cycle. Low P(4) was not a prerequisite for elevated PRL. Although elevated (> or =10ng/mL) PRL (20.9+/-2.0ng/mL) occurred more often with low (<2ng/mL) P(4) (20 of 24 cases) it also occurred with P(4) above 3ng/mL in two affected bitches and in two control bitches. Whether the occurrence of relatively low PRL concentrations (<4ng/mL) in samples obtained from 4 of the 35 pseudopregnant bitches reflected variable and often elevated PRL secretion or increased sensitivity to PRL in the absence of elevated prolactin in those animals was not determined. We inferred that elevated plasma PRL was often involved in the etiology of overt PSP; furthermore, a premature decline in circulating P(4) concentrations may be a factor in some instances.

Effects of dose and duration of continuous GnRH-agonist treatment on induction of estrus in beagle dogs: competing and concurrent up-regulation and down-regulation of LH release.

Dose-response estrus-induction trials were conducted during anestrus in 93 treated and 6 control bitches, a continuous administration of the GnRH-agonist lutrelin with a potency 150 x GnRH, and at six different doses from 0.2 to 4.8 microg/kg/d for 7-14 days in 15 groups of six to eight dogs each in defined stages of natural or pharmacologically determined anestrus. Agonist treatment induced clinically and cytologically normal proestrus (in 89% of cases) within 4.8 +/- 0.2 x days, and resulted in behavioral estrus (71%), spontaneous late-proestrus LH (and FSH) surges, ovulation (59%) and pregnancy (44%) in a dose dependent manner. Outcomes of ovulation and pregnancy in most cases required that the dose be sufficiently large enough to routinely stimulate a large initial increase in LH and FSH (i.e., > or = 0.6 microg/kg/d), and of sufficient duration (i.e., > 7 days) to ensure that supra-basal gonadotropin levels persistedntil no longer needed for spontaneous continuation of an induced proestrus. Success additionally required that the GnRH dose be modest enough (i.e., < 1.8 microg/kg/d) to not excessively down-regulate spontaneous pre-ovulatory surge release of gonadotropin or be removed shortly before or at the time when the LH surges typically occurred (10-13 days after initiation of treatment). The 1.8 microg dose was compared to saline to assess the time course of its down-regulation action on serum LH in six ovariohysterectomized bitches compared to four saline-related controls. Results in intact bitches receiving the 1.8-microg doses demonstrated an LH-releasing effect for 10-11 days that overlapped a period of obvious down-regulation seen with the same dose after 3 days in the ovariohysterectomized bitches. In the latter, however, complete down-regulation to anestrus-like values did not occur until after 18-21 days of treatment. A dose of 0.6 microg/kg/d for 12 days yielded the best estrus-induction results, including pregnancy rates of 100% in six bitches treated in natural-anestrus bitches, six bitches in which anestrus had been advanced by a luteolytic prostaglandin treatment and in six bitches in which anestrus had been extended by progesterone implants administered for 3 months. Although lutrelin is not commercially available, these results provide guidelines for the development of estrus-inducing protocols with other GnRH-agonists of known biopotencies.

Relation between mating or ovulation and the duration of gestation in dogs.

The effects of day of mating and litter size on gestation length in dogs were studied in 36 beagle bitches (age 2-10 yr). The day that plasma progesterone concentrations exceeded 2 ng/mL was considered the day of ovulation; dogs were randomly assigned to be bred once, 1-5 days after the estimated day of ovulation. The interval from mating to parturition was negatively correlated with the number of days from estimated ovulation to mating (P < 0.01). Gestation length (interval from ovulation to parturition) was almost constant at 63.9 +/- 0.2 days (mean +/- S.E.M.), with no significant relationship between the number of fetuses and the duration of gestation.

Gross and histopathologic effects of medroxyprogesterone acetate and progesterone on the mammary glands of adult beagle bitches.

Adult beagle bitches received 0.2 to 75 mg/kg doses of medroxyprogesterone acetate (MPA) once every 3 months for 1 to 1.5 years. Doses greater than 2.0 mg/kg prevented the recurrence of ovarian cycles; lower doses did not. MPA (10 and 75 mg/kg) induced a dose-related development of multiple, large (greater than 5 mm diameter) mammary nodules that occurred earlier in older dogs than in younger dogs. MPA-induced mammary hyperplasia and nonnodular dysplasias were also noted. Most of the large (5 to 110 mm in diameter) MPA-induced nodules were, in nearly equal numbers, nodules of lobular hyperplasia, simple adenomas, or complex adenomas. Such benign mammopathies all appear to have histopathologic counterparts in human breast disease. However, simple adenomas are uncommon in both humans and dogs. Some of the MPA-induced nodules were benign mixed tumors with cartilaginous metaplasia. No malignant tumors were found. Induction of mammary tumors by 75 mg MPA/kg was not affected by prior ovariectomy but was reached by prior hypophysectomy, suggesting involvement of pituitary secretion in MPA-induced mammary gland disease.

Serial ultrasonographic appearance of postpartum uterine involution in beagle dogs.

Postpartum changes in uterine shape, architecture, echogenicity and diameter were determined during the serial examinations of five beagle bitches. During postpartum Week 1, the uterine horns were tubular structures composed of multiple layers of various echogenicity and had multiple, discrete enlargements with hypoechoic centers at placental sites. Diameters ranged from 1.1 to 3.8 cm at placental site enlargements, and 0.5 to 1.4 cm between enlargements. Uterine involution appeared to be completed by 15 wk post partum. At 15 weeks the uterine horns of each dog were uniform hypoechoic, tubular structures without enlargements and had a reduced diameter of 0.3 to 0.6 cm. These ultrasonographic findings are similar to previously reported gross and light microscopic descriptions of canine uterine involution.

Association between the preovulatory luteinizing hormone surge and the early ultrasonographic detection of pregnancy and fetal heartbeats in beagle dogs.

The size of the gestational sac and embryonic mass as well as the embryonic heartbeat were examined ultrasonographically from Day 16 to 25 of pregnancy in 15 beagle bitches, using a 7.5 MHz transducer. Results were more consistent when gestational age was based on the day of the preovulatory luteinizing hormone (LH) surge than on the day of first breeding. The gestational sac was first detected at 17 to 20 d after the LH surge, when it was 1 to 2 mm in diameter and 1 to 4 mm in length. The diameter and length of the gestational sac increased exponentially. At Day 25, the mean diameter was 8.2 +/- 0.3 mm (7 to 9 mm) and mean length was 20.3 +/- 1.1 mm (14 to 24 mm). Embryonic mass and heartbeat were first detected at 23 to 25 d after the LH surge. The embryonic heartbeat was detected on the day of or the day after detection of the embryonic mass, at which time the embryonic mass was 1 to 4 mm in length and was located at the periphery of the gestational sac.

Effect of stage of anestrus on the induction of estrus by the dopamine agonist cabergoline in dogs.

Beagle bitches were administered the dopamine D2 receptor agonist cabergoline in 3 groups of 5 animals each, starting on known days of the estrous cycle. Cabergoline treatment was started in either early anestrus (Days 93 to 108), mid-anestrus (Days 123 to 156), or late anestrus (Days 161 to 192) at doses of 5 ug/kg/d, per os, and was continued until the confirmation of induced proestrus or for 40 d. Reproductive parameters were compared with those in 5 control anestrous bitches (Days 90 to 150). In control bitches, the mean (+/- SEM) interval to the next proestrus (73+/-11 d) resulted in an interestrus interval (192+/-9 d) similar to that of the previous cycles (196+/-11 d). In 14 of the 15 cabergoline-treated bitches, the next proestrus occurred within 4 to 30 d, was premature in early and mid-anestrous bitches and developed with low variability within groups. The resulting intervals to proestrus in bitches treated with cabergoline in early anestrus (20+/-2 d), mid-anestrus (14+/-3 d) and late anestrus (6+/-1 d) resulted in interestrus intervals in those groups of 131+/-5, 166+/-7 and 196+/-2 d, respectively. In response to treatment, interestrus intervals were reduced (P<0.05) and more synchronous (P<0.05) in early and mid-anestrus bitches, and were more synchronous (P<0.05) in late-anestrous bitches compared with those of control bitches or those of the previous cycle. Periovulatory estradiol and progesterone profiles of induced cycles in treated bitches were similar to those of spontaneous cycles in control bitches. Four of 5 control bitches and 12 of the 14 responding cabergoline-treated bitches became pregnant and produced normal litters. Plasma prolactin concentrations at Days 2 and 5 of treatment (0.3+/-0.1 ng/mL) and at the onset of proestrus shortly before the end of treatment (0.4+/-0.1 ng/mL) were lower (P<0.05) than those present in anestrus prior to treatment (1.7+/-0.6 ng/mL) or in control bitches. Prolactin was also low at the onset of proestrus in control bitches (0.5+/-0.2 ng/mL). The results demonstrate that prolactin-lowering doses of the dopamine agonist cabergoline can terminate the normal obligate anestrus in dogs, and that the effect occurs more slowly in early anestrus than in mid or late anestrus.

Determination of ovulation time in bitches based on teasing, vaginal cytology, and elisa for progesterone.

The estrous cycle of 16 mature mongrel female dogs was monitored to evaluate the accuracy of teasing, vaginal cytology and quantitative ELISA progesterone assay to determine ovulation. The dogs were presented to male, and blood samples and vaginal swabs were taken daily during proestrus and estrus. Selected serum samples collected during estrus were assayed for endogenous LH by radioimmunoassay (RIA). Plasma samples collected during proestrus and estrus were assayed for progesterone with a commercially available ELISA kit. Ovulation was considered to take place 48 h after the preovulatory LH peak. Vaginal cytology smears were stained with Wright's stain and evaluated for the percentage of superficial squamous cells. Day 1 of diestrus (Day 1) was defined as a drop of 20% or more in the total number of superficial cells. Two standard curves (linear and best fitted curves) commonly used with ELISA were compared together and with the RIA progesterone assay. Ovulation was estimated to occur when progesterone concentration was 4.9 +/- 1.0 ng/ml (mean +/- SD, n = 15), with a range of 3.4 to 6.6 ng/ml. Based on vaginal cytology, ovulation took place 6.9 +/- 1.6 d (n = 15) after 80% of the squamous cells were superficial and 6.8 +/- 1.4 d (n = 16) before Day 1. Ovulation took place 2.1 +/- 3.9 d (n=11) after the first day of standing estrus and 8.8 +/- 1.5 d (n = 10) before the last day of receptivity. The two standard curves were found parallel to each other and to the RIA progesterone assay. Based on the results of the present study, ELISA progesterone assay and determination of the first day of estrus by vaginal cytology are reliable methods for predicting ovulation, whereas the last day of receptivity as determined by teasing and Day 1 as determined by vaginal cytology are reliable methods to retrospectively estimate ovulation time.

Estrus induction in the bitch using a combination diethylstilbestrol and FSH-P.

The purpose of the study was to induce estrus and ovulation in normal bitches using a combination of diethylstilbestrol (DES) and follicle stimulating hormone of porcine pituitary origin (FSH-P). Thirteen mature mongrel female dogs were divided into two groups, the first group was treated for estrus induction during late anestrus and the second group during mid-anestrus. The dogs were monitored by teasing, vaginal cytology, and hormonal assay during the induced (n=13) and the previous spontaneous estrous cycle (n=9). Six of eight and three of five bitches came into standing estrus in the first and second group, respectively. Of the bitches that came into estrus, three conceived in the first group and one in the second. The average induced litter size was 7.0 versus 7.5 for the colony. Based on vaginal cytology the induced proestrus and estrus lasted 1.7 (0 to 3) and 12.9 (4 to 24) d, respectively, while the spontaneous proestrus and estrus lasted 5.8 (0-17) and 12.8 (9-15) d, respectively. Progesterone profiles were similar between the induced and spontaneous estrous cycles, although the progesterone peak was higher during the spontaneous cycle. The preovulatory luteinizing hormone (LH) surge was observed in only one induced estrous cycle. Modest results were obtained with this therapy. However, the litter sizes were normal and the induced cycles were very similar to the physiologic ones. No side effects were seen with the oral form of DES.

Induction of estrus in bitches with normal and persistent anestrus using human menopausal gonadotropin (hMG).

Human menopausal gonadotropin (hMG) was administered intramuscularly to 10 bitches during apparently normal anestrus (n = 7) or persistent anestrus (n = 3). Each dog received a 75-IU dose of hMG (75 IU LH and 75 IU FSH; 1 to 7 units/kg) daily for nine days. Nine bitches responded with obvious signs of proestrus within 3 to 9 days. Of these, 3 bitches exhibited a weak proestrus while 2 exhibited a normal estrus and ovulation but failed to become pregnant The remaining 4 bitches became pregnant at the induced cycle and produced normal litters at 72 to 85 d after the start of treatment, including 1 bitch that had been treated at 24 mo after the last estrus. In 2 cases, treatment resulted in ovulation following 25 or 34 mo of chronic pubertal anestrus, 1 of which became pregnant. The results suggest that hMG can be a useful gonadotropin preparation for inducing estrus in dogs.

Pregnancy-specific elevations in fecal concentrations of estradiol, testosterone and progesterone in the domestic dog (Canis familiaris).

Estradiol (E2), testosterone (T) and progesterone (P4) concentrations were determined by enzyme-immunoassay in aqueous extracts of fecal samples obtained during anestrus, proestrus, estrus and metestrus of 11 nonpregnant and 11 pregnant bitches. Fecal hormone concentrations (ng/g) changed in relation to stage of cycle. Mean fecal steroid concentrations in 22 anestrous bitches and 3 ovariectomized bitches were low and similar for E2 (53 +/- 5 and 27 +/- 2), T (60 +/- 7 and 36 +/- 6), and P4 (62 +/- 6 and 86 +/- 15). Within 0 to 3 d of the ovulatory LH surge fecal E2 reached peak concentrations (301 +/- 38). The T peaks (281 +/- 41) were coincident or 1 to 3 d later. Fecal P4 was then elevated for approximately 2 m.o. Between Days 26 and 45 after ovulation, mean fecal P4 concentrations were higher (P < 0.05) in pregnant (401 +/- 60) than in nonpregnant bitches (164 +/- 23) and peak fecal P4 concentrations in individual animals were higher (P < 0.01) in pregnant (812 +/- 121) than in nonpregnant bitches (425 +/- 97). In the same period mean concentrations of E2 (117 +/- 13 vs 61 +/- 5) and T (102 +/- 10 vs 70 +/- 6) were also higher (P < or = 0.05) in pregnant than in nonpregnant bitches. Serum E2, T and P4 concentration were positively correlated (P = 0.1) with concentration in fecal samples obtained one day after serum collection. Although serial fecal ovarian steroid concentrations demonstrate the time course of ovulatory cycles, the diagnostic value of individual fecal samples appears limited. The ratios of peak to basal values were approximately 6, 5 and 7 for E2, T and P4, respectively, and were considerably lower than ratios of 12 to 50 previously reported for serum or plasma concentrations. The results demonstrate that there are pregnancy-specific increases in P4, E2 and T production reflected in fecal concentrations. While such increases are reflected in fecal samples, they are generally not evident in serum or plasma concentrations because of increased hemodilution, metabolism and clearance in pregnant bitches. The physiological stimulus for these increases, presumably ovarian in origin, or the potential role of prolactin is not known.

Control of luteal function and implantation in the mink by prolactin.

Mink (Mustela vison) were treated during the period of embryonic diapause with prolactin or ergocryptine (CB-154). Prolactin advanced implantation time and hastened onset of luteal phase progesterone secretion. Duration of gestation in prolactin-treated adult mink was shorter than that of control mink. Ergocryptine had the opposite effects, prolonging gestation and inhibiting onset of luteal phase progesterone secretion. Prolactin is suggested to be the luteotrophin necessary for termination of embryonic diapause in mink.

Postimplantation increase in plasma fibrinogen concentration with increase in relaxin concentration in pregnant dogs.

OBJECTIVE: To determine time courses of pregnancy-related changes in plasma fibrinogen, serum relaxin, and serum C-reactive protein-like immunoreactivity (CRP-LI) concentrations in pregnant and nonpregnant dogs. ANIMALS: 16 pregnant and 13 nonpregnant Beagles, 6 pregnant Beagles, and 3 pregnant and 3 nonpregnant dogs of other breeds. PROCEDURE: Fibrinogen was measured by nephelometric centrifugal analysis of light scatter in plasma samples of all dogs, and CRP-LI was measured by fluorescence immunoassay in selected sera from 10 pregnant and 10 nonpregnant dogs. Relaxin was measured in selected sera from 7 pregnant and 7 nonpregnant dogs. RESULTS: During pregnancy, fibrinogen concentration increased between days 21 and 30 after the luteinizing hormone surge, and was > 280 mg/dl between days 29 and 50 in 84 of 86 samples, with peak values 539 +/- 29 mg/ dl higher (P < 0.01) than those in nonpregnant dogs (188 +/- 8 mg/dl), higher values from days 21 to 50 (P < 0.01) than those in nonpregnant dogs, and values similar to those in nonpregnant dogs after day 50. Relaxin concentration was increased from days 26 to 30 and 0 to 4 days after fibrinogen concentration increased in pregnant dogs, and was not detectable in nonpregnant dogs. The CRP-LI concentration was higher in pregnant dogs at days 26 to 50, but values were inconsistent within and among dogs, and near the limit of sensitivity of the assay. CONCLUSIONS: Concentration of the acute-phase reactant protein fibrinogen increases after day 20 following implantation in dogs, at or just before the pregnancy-specific increase in relaxin concentration from days 26 to 30, and persists until day 50. CLINICAL RELEVANCE: Fibrinogen assay may be useful for pregnancy diagnosis in dogs.

Ultrasonographic appearance of the uterus, placenta, fetus, and fetal membranes throughout accurately timed pregnancy in beagles.

Serial ultrasonographic examinations were performed on 8 Beagle bitches from 20 to 60 days pregnant to determine time of first detection, appearance, and sizes of selected features of pregnancy. Gestation was timed from the day of the preovulatory luteinizing hormone surge. Findings related to gestational age were consistent among bitches. Gestational ages at earliest detection of the following features were: chorionic cavity at day 20; placental layers in the uterine wall at day 22 to 24; zonary placenta at day 27 to 30; embryo and heartbeat at day 23 to 25; yolk sac membrane at day 25 to 28; allantoic membrane at day 27 to 31; choroid plexus of the brain at day 31 to 35; fetal movement at day 34 to 36; skeleton at day 33 to 39; bladder and stomach at day 35 to 39; kidney at day 39 to 47; and liver hypoechoic, compared with lung, at day 38 to 42. Extra-fetal structures were measurable from day 20 or 22 through day 48. Chorionic cavity diameter increased from 0.2 +/- 0.0 cm to 3.3 +/- 0.2 cm, outer uterine diameter increased from 0.8 +/- 0.03 cm to 4.8 +/- 0.2 cm, length of chorionic cavity or zonary placenta increased from 0.3 +/- 0.03 cm to 4.9 +/- 0.05 cm, uterine wall thickness increased from 0.3 +/- 0.03 cm to 0.8 +/- 0.01 cm, and placental thickness increased from 0.1 +/- 0.0 cm to 0.5 +/- 0.05 cm. Chorionic cavity diameter, outer uterine diameter, and placental length each increased at a linear rate through day 37, after which time, each had a marked plateau in growth. Of the extra-fetal structures, chorionic cavity diameter was the most accurate for estimation of gestational age. All of the fetal structures studied increased at an increasing (second order) rate. Crown-rump length increased from 0.3 +/- 0.05 cm on day 24 to 9.2 +/- 0.2 cm on day 48. Body diameter increased from 0.2 +/- 0.03 cm on day 24 to 4.6 +/- 0.15 cm on day 60. Head diameter increased from 0.8 +/- 0.05 cm on day 34 to 2.7 +/- 0.04 cm on day 60. Of the fetal structures, head diameter was the most accurate for estimation of gestational age.

Effects of propranolol on thyroid function in the dog.

The effect of propranolol on thyroid function was evaluated in 6 mature euthyroid Beagles. Propranolol was administered orally in doses of 20 mg given 3 times daily for 2 weeks and then increased to 40 mg given 3 times daily for an additional 2 weeks. Six age- and sex-matched, euthyroid Beagles served as controls. Serum base-line concentrations of tetraiodothyronine (T4), triiodothyronine (T3), and reverse triiodothyronine (rT3) were measured before propranolol administration and at weekly intervals thereafter. Thyroid response to 5 IU of aqueous thyroid stimulating hormone administered IV was monitored before propranolol administration and at the 2- and 4-week treatment intervals. The T4, T3, and rT3 concentrations were measured by radioimmunoassay. There were no significant differences in base-line or postthyroid stimulating hormone serum concentrations of T4, T3, or rT3 in any individual or between the treatment or control groups at any treatment interval (P greater than 0.05). Seemingly, the therapeutic use of propranolol in euthyroid dogs should not alter thyroid hormone metabolism.