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Objective: To evaluate gonadotropin secretion and ovarian function after administration of deslorelin acetate to induce ovulation in mares., Design: Randomized controlled trial., Animals: 16 healthy mares with normal estrous cycles., Procedure: 8 control mares were allowed to ovulate spontaneously, whereas 8 study mares received deslorelin to induce ovulation when an ovarian follicle > 35 mm in diameter was detected. Follicle development and serum concentrations of gonadotropins were monitored daily during 1 estrous cycle. Pituitary responsiveness to administration of gonadotropin-releasing hormone (GnRH) was evaluated 10 days after initial ovulation., Results: Interovulatory intervals of mares treated with deslorelin (mean +/- SD, 25.6 +/- 2.6 days) were longer than those of control mares (22.9 +/- 1.8 days). Diameter of the largest follicle was significantly smaller during 2 days of the diestrous period after ovulation in deslorelin-treated mares than in control mares. Concentrations of follicle-stimulating hormone (FSH) were lower in deslorelin-treated mares on days 5 through 14 than in control mares. Concentrations of luteinizing hormone were not different between groups during most of the cycle. Gonadotropin release in response to administration of GnRH was lower in mares treated with deslorelin acetate than in control mares., Conclusions and Clinical Relevance: Administration of deslorelin was associated with reduction in circulating concentrations of FSH and gonadotropin response to administration of GnRH during the estrous cycle. Low concentration of FSH in treated mares may lead to delayed follicular development and an increased interovulatory interval.

Concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured in serum samples obtained from 100 dogs. Groups (n = 25/group) consisted of sexually intact and ovariohysterectomized bitches and sexually intact and castrated male dogs. Mean (+/- SD) concentrations of LH in the serum of sexually intact and ovariohysterectomized bitches were 1.2 (+/- 0.9) and 28.7 (+/- 25.8) ng/ml, respectively. Mean concentrations of FSH in the serum of sexually intact and ovariohysterectomized bitches were 98 (+/- 49) and 1,219 (+/- 763) ng/ml, respectively. Mean concentrations of LH in the serum of sexually intact and castrated male dogs were 6.0 (+/- 5.2) and 17.1 (+/- 9.9) ng/ml, respectively. Mean concentrations of FSH in the serum of sexually intact and castrated male dogs were 89 (+/- 28) and 858 (+/- 674) ng/ml, respectively. In addition to history, physical examination results, and other laboratory values, the measurement of serum gonadotropin concentrations may aid in determining whether dogs have been neutered.

A specific radioimmunoassay was used to measure concentrations of hydrocortisone (cortisol) in the serum and plasma of 4 dogs. Differences (P greater than 0.05) in concentrations of cortisol were not found between serum and plasma (from EDTA-treated and heparinized blood samples). Differences (P greater than 0.05) in serum or plasma concentrations of cortisol were not found between samples stored at 4 C for various times (10 minutes, 10 hours, 40 hours) after collection, but before removal of RBC. In a study designed to determine the stability of cortisol in serum samples stored at room temperature, degradation was dependent on the initial serum concentrations of cortisol. Decreases (P greater than 0.05) did not occur in concentrations of cortisol in serum samples stored up to 15 days when initial concentrations of cortisol were less than 15 ng/ml. However, when initial concentrations of cortisol were approximately 55 ng/ml and 80 ng/ml, significant (P greater than 0.05) degradation occurred after 9 and 5 days of storage, respectively. Results of this investigation indicate that either serum or plasma of dogs is suitable for radioimmunoassay of cortisol and that samples (with and without added coagulants) incubated at 4 C may be left uncentrifuged for up to 40 hours without cortisol degradation. However, prolonged storage of serum at room temperature is detrimental, particularly for samples having large concentrations of cortisol.

Serum testosterone concentrations in samples collected daily from 6 bitches for at least 60 days before the onset of diestrus were determined by radioimmunoassay. Mean serum concentrations (+/- SEM) of testosterone ranged from 31 +/- 11 to 141 +/- 63 pg/ml during late anestrus. Mean testosterone concentrations during proestrus ranged from 106 +/- 29 to 239 +/- 113 pg/ml, with the highest concentration (526 +/- 225 pg/ml) occurring the day of the preovulatory surge of luteinizing hormone. Although the ovaries may be sites of production during late anestrus, proestrus, estrus, and early diestrus, further investigation is necessary to determine whether testosterone has an important physiologic or endocrinologic function in the bitch (ie, sexual behavior, vaginal hypertrophy, and luteinizing hormone surge).

Response to thyrotropin (TSH) was evaluated in 2 groups of mixed-breed dogs. Thyrotropin (5 IU) was administered IV to dogs in group 1 (n = 15) and IM to dogs in group 2 (n = 15). Venous blood samples were collected immediately before administration of TSH and at 2-hour intervals for 12 hours thereafter. In group 1, the maximum mean concentration (+/- SD) of thyroxine (T4; 7.76 +/- 2.60 micrograms/dl) and 3,5,3'-triiodothyroxine (T3; 1.56 +/- 0.51 ng/ml) was attained at postinjection hours (PIH) 8 and 6, respectively. However, the mean concentration of T4 at PIH 6 (7.21 +/- 2.39 micrograms/dl) was not different (P greater than 0.05) from the mean concentration at PIH 8. The maximum mean concentration of T4 (10.10 +/- 3.50 micrograms/dl) and T3 (2.22 +/- 1.24 ng/ml) in group 2 was attained at PIH 12 and 10, respectively. Because dogs given TSH by the IM route manifested pain during injection, had variable serum concentrations of T3 after TSH administration, and may require 5 IU to achieve maximal increases in serum T4 concentrations, IV administration of TSH is recommended. The optimal sampling time to observe maximal increases in T3 and T4 after IV administration of TSH was 6 hours. Repeat IV administration of TSH may cause anaphylaxis and, therefore, is not recommended.

Concentrations of total carnitine (free and esterified) were determined in seminal fluids from 12 normospermic dogs before treatment and from the same 12 dogs after assignment to control, vasectomized, or castrated treatment groups (4 dogs each). Before treatment, the mean concentration (+/- SD) of carnitine in seminal fluid was 946 +/- 345 nmol/ml and was not significantly different (P greater than 0.05) among groups on any seminal collection day. After surgery, mean concentrations of carnitine in seminal fluid from vasectomized and castrated dogs were 49 +/- 9 and 14 +/- 5 nmol/ml, respectively and were lower (P less than 0.001) than the mean concentration in control (sexually intact) dogs. Dogs with obstructive azoospermia may be distinguished from those with aspermatogenesis (secretory azoospermia) by measuring seminal carnitine concentration. Seemingly, the epididymis is the major source of carnitine in canine seminal fluid, because the concentration of carnitine in prostatic fluid was only 58 +/- 53 nmol/ml, whereas the concentration of carnitine in 6 pools of epididymal fluid was 18.8 +/- 3.9 mumol/ml.

Three groups of bitches were treated with diethylstilbestrol (75 micrograms/kg) orally for 7 days (n = 12), estradiol cypionate intramuscularly once (22 micrograms/kg; n = 12), or estradiol cypionate intramuscularly once (44 micrograms/kg; n = 12). Treatments commenced during late proestrus (n = 4/group), the fourth day of behavioral estrus (n = 4/group), or the second day of diestrus (n = 4/group). All bitches were bred on alternate days throughout estrus to stud dogs of known fertility. Ovariohysterectomies were performed on day 25 of diestrus to diagnose pregnancy and to assess any pathologic changes in the uterus. Eleven bitches treated with diethylstilbestrol, 6 bitches treated with the low dosage of estradiol cypionate, and 4 bitches receiving the high dosage of estradiol cypionate were pregnant at the time of surgery. Ten of the bitches treated with estrogens during proestrus, 6 treated during estrus, and 4 treated during diestrus were pregnant. The serum concentration of progesterone in 2 bitches treated with the high dosage of estradiol cypionate decreased to less than 2 ng/ml by day 25 of diestrus, suggesting premature luteal regression. Diethylstilbestrol appeared to have little efficacy in terminating pregnancy. Estradiol cypionate appeared to have greater efficacy when administered during estrus or early diestrus; however, pyometra developed in 2 bitches treated with this estrogen during diestrus.

Blood was collected from 6 adult bitches (3 pregnant and 3 nonpregnant) daily for 59 days after the onset of diestrus, and serum progesterone concentrations were determined. The bitches were hysterectomized at various times during diestrus [diestrus day (DD) 5, 15, or 25] to determine whether the uterus has a role in maintaining luteal function in the pregnant or nonpregnant bitch. Concentrations of serum luteinizing hormone (LH) were also measured to determine whether LH concentrations decrease when luteal function abates (experiment 1). All 6 bitches in experiment 1 had progesterone concentrations greater than 1.0 ng/ml during the 2-month period, indicating that neither the pregnant nor nonpregnant uterus was necessary for maintaining luteal function in the bitch. Concentrations of LH appeared to increase in the serum of 5 of the 6 bitches when progesterone concentrations were declining, indicating that cessation of luteal function does not appear to result from a lack of LH. Blood was collected from the 6 bitches used in experiment 1 twice weekly during the 2nd diestrus after hysterectomy (experiment 2) to determine whether alterations in luteal function that might be observed during experiment 1 were due to some aspect of the surgical procedure, rather than to absence of a uterus. Progesterone concentrations in the serum were lower (P less than 0.05) during the 10 days after surgery in the 2 bitches hysterectomized on DD 5 than in the 4 bitches remaining intact during this period (experiment 1).(ABSTRACT TRUNCATED AT 250 WORDS)

Receptors for estrogen and progesterone were measured in cytosols prepared from specimens of canine endometrium obtained at late proestrus, day 4 of estrus, day 2 of diestrus, and at 10 day intervals from days 10 through 80 of diestrus. Twenty nine adult bitches were used, with 2 to 4 dogs used at each time point. Concentrations of estradiol receptors measured in endometrial cytosols from late proestrus through day 10 of diestrus were similar (mean +/- SEM: 9.9 +/- 2.2, 10.5 +/- 1.2, 16.3 +/- 1.6, and 16.2 +/- 2.9 pmol/g of tissue at proestrus, day 4 of estrus, days 2 and 10 of diestrus, respectively). As serum concentrations of progesterone increased during early diestrus, the concentration of estradiol receptors decreased and were significantly (P less than 0.05) lower on days 30 (4.9 +/- 1.3 pmol/g of tissue) and 40 (3.7 +/- 0.6 pmol/g of tissue) of diestrus. After day 40 of diestrus, when serum concentrations of progesterone were approaching basal concentrations, the concentration of estradiol receptors increased and remained significantly (P less than 0.05) higher from days 60 to 80 of diestrus (day 60, 13.4 +/- 2.9; day 70, 15.7 +/- 1.7; day 80, 19.8 +/- 2.4 pmol/g of tissue). As observed for estrogen receptors, the concentration of endometrial receptors for progesterone also gradually increased from late proestrus (4.9 +/- 1.3 pmol/g of tissue) to day 2 of diestrus (6.4 +/- 0.3 pmol/g of tissue).(ABSTRACT TRUNCATED AT 250 WORDS)

Serum concentrations of thyrotropin (TSH), prolactin, thyroxine, and 3,5,3'-triiodothyronine in 15 euthyroid dogs and 5 thyroidectomized and propylthiouracil-treated dogs after thyrotropin-releasing hormone (TRH) administration were measured. Although thyroidectomized and propylthiouracil-treated dogs had higher (P less than 0.01) base-line concentrations of TSH in serum than did euthyroid dogs, concentrations of TSH after TRH administration varied at 7.5, 15, and 30 minutes with 14 of 45 samples obtained from healthy dogs having lower TSH concentrations than before TRH challenge. Similarly, concentrations of 3,5,3'-triiodothyronine in the serum of euthyroid dogs 4 hours after TRH administration were similar (P less than 0.05) to concentrations before TRH challenge. Although the mean concentration of thyroxine in serum was elevated (P less than 0.05) 4 hours after administration of TRH to euthyroid animals, as compared with base-line levels, the individual response was variable with concentrations not changing or decreasing in 4 dogs. Therefore, the TRH challenge test as performed in the current investigation was of limited value in evaluating canine pituitary gland function. Although mean concentrations of TSH in serum were higher (P less than 0.05) in euthyroid dogs after TRH administration, the response was too variable among individual animals for accurate evaluation of pituitary gland function. Concentrations of prolactin in the sera of dogs after TRH administration, confirmed previous reports that exogenously administered TRH results in prolactin release from the canine pituitary and indicated that the TRH used was biologically potent.

Equilibrium, double-antibody radioimmunoassay (RIA) procedures were validated to measure concentrations of prostaglandin (PG) F2 alpha, and E2 in canine plasma and endometrium. The procedure for measuring PGF2 alpha or PGE2 used [125I]PGF2 alpha or [3H]PGE2, respectively, as radiolabeled antigens. Specificity was demonstrated by determining the relative potency of selected PG. Relative potencies were calculated by dividing the mass of PGF2 alpha or PGE2 producing 50% inhibition of maximum bound tubes (Bo) by the quantity of test PG producing 50% inhibition in the same assay. Only PGF1 alpha and PGE1 had relative potencies of greater than 1.0% in the PGF2 alpha and PGE2 RIA, respectively. To assess the accuracy of the 2 assay systems, known amounts of authentic hormone were added to plasma, tissue, or 0.05M phosphate-buffered saline solution containing 0.1% gelatin (gel-PBSS). When increasing amounts of PGF2 alpha or PGE2 were added to plasma, tissue, or gel-PBSS, concentrations of PG assayed from extracted or extracted plus chromatographed samples were similar. Additionally, PGF1 alpha or PGE1 was not detected in canine plasma or tissue; therefore, extraction was the only purification needed before analysis of PGF2 alpha or PGE2. The intra-assay precision of 10 assay replicates for a low (70% Bo) and high (27% Bo) sample was 16.0% and 6.7% (coefficient of variation), respectively, for the PGF2 alpha assay. The intra-assay precision of 3 assay replicates for a low (80% Bo) and high (32% Bo) sample was 7.6% and 4.4%, respectively, for the PGE2 assay.(ABSTRACT TRUNCATED AT 250 WORDS)