H. D. Hafs

Progesterone, LH, Estrus and Ovulation after Prostaglandin F2α in Heifers

Summary PGF2α (30 mg Tham salt) was injected im into five heifers during diestrus (Days 9 to 13 of the estrous cycle), im into six heifers during metestrus (Day 3), and intravaginally into six heifers during diestrus. After im PGF2α during diestrus, (a) luteal diameter decreased from 2.3 ± 0.1 cm to 1.8 ± 0.1 cm at 24 hr and to 0.6 ± 0.3 cm at 72 hr, (b) blood serum progesterone fell from 4.0 ± 0.4 ng/ml to 1.5 ± 0.2 ng/ml at 12 hr and to 1.0 ± 0.2 ng/ml at 72 hr, and (c) estrus began at 74 ± 3 hr and ovulation occurred at 104 ± 6 hr. After intravaginal PGF2α during diestrus, one heifer failed to respond; the other five responded similarly to those given im PGF2α during diestrus except that luteolysis was more variable and delayed about 1 or 2 days compared to that after im PGF2α. PGF2α (im) was neither luteolytic nor luteostatic in metestrus. We conclude that 30 mg PGF2α is luteolytic during diestrus in heifers, but im administration is more effective than intravaginal administration.

Sperm capacitation by uterine fluid or beta-amylase in vitro.

Rabbit sperm developed the capacity to fertilize ova when incubated in utero or in vitro in fluids from estrous uteri. Incubation of sperm with beta-amylase in phosphate-buffered Lockes solution also resulted in capacitation. The data suggest that sperm capacitation involves enzymatic alteration of carbo-hydrate-containing seminal macromolecules which coat sperm and inhibit fertilization.

Androgen secretion and spermatogenesis in rats following semistarvation.

Summary Male Sprague-Dawley rats were allowed to feed freely until 10 weeks of age and then were restricted to 50% of the ad libitum food intake of controls for 8 or 23 weeks. Serum testosterone, determined by gas-liquid chromatography, decreased during the first 8 weeks of food restriction to 31% of that in full-fed controls, but then rebounded to control levels following another 15 weeks of semistarvation. Similarly, weights and secretory activities of accessory reproductive organs declined during the first 8 weeks and increased during the last 15 weeks of food restriction. When allowed to refeed for 3 weeks following 20 weeks of semistarvation, serum testosterone rose to 3.0 ng/ml, twice the 1.5 ng/ml in fully fed controls and three times the 1.2 ng/ml for chronically semistarved rats at the same age. The complete absence of food from previously full-fed rats for 6 days lowered testosterone levels to undetectable quantities. Absolute weights of testes and epididymides and their concentration of sperm (per gram of tissue) were affected less than androgens during a 50% reduction in feed intake as well as during the subsequent ad libitum refeeding period.

Bovine Serum LH, GH, and Prolactin During Late Pregnancy, Parturition and Early Lactation

Summary Jugular blood was collected from 34 Holstein heifers from 26 days before parturition until 26 days postpartum or until first estrus. Serum prolactin varied between 80 and 110 ng/ml until Day 2 prepartum when it increased markedly to peak of 285 ng/ml at 1 day prepartum. Prolactin decreased linearly (p < 0.01) from the peak until 2 days after calving, stabilized at about 90 ng/ml until Day 9, and gradually declined until day 26 (36 ng/ml). Postpartum (Day 5-26) prolactin was lower (p < 0.05) than prepartum (Day 26-5) prolactin. Growth hormone followed a pattern similar to prolactin but peaked 24 hr later, at parturition, and decreased from the peak to concentrations characteristic of prepartum values by Day 4 postpartum. Serum growth hormone during late pregnancy (Day 26-5) was lower (p < 0.05) than during early lactation (Day 5-26). Serum LH was consistently low (0.4-0.8 ng/ml) until Day 9 postpartum when it increased to about 1.5 ng/ml until first estrus.

Luteolysis, estrus and ovulation, and blood prostaglandin F after intramuscular administration of 15, 30 or 60 mg prostaglandin F2α

During diestrus in three consecutive estrous cycles, each of six heifers was given (im) 30 mg, 15 mg (twice at 6-hr intervals) and 60 mg prostaglandin F2alpha (PGF2alpha) tham salt. Neither the decline in blood progesterone, the increase in blood estradiol, the duration or the peak of the LH surge, the interval to onset of estrus, nor the interval to ovulation was affected significantly by dose of PGF2alpha. Thus, relative to that after 30 mg PGF2alpha im, two injections of 15 mg at 6-hr intervals or 60 mg PGF2alpha did not hasten luteolysis. Thirty mg was an ample in dose of PGF2alpha to cause luteolysis. Regardless of im dose of PGF2alpha, blood PGF peaked at about 6.0 ng/ml within 10 minutes and returned to basal values (less than 1.0 ng/ml) within 90 minutes. In another trial, after a single iv injection of 5 mg PGF2alpha, blood PGF peaked (25 ng/ml) within 5 minutes and returned to basal values within 15 minutes. During a 30-minute infusion (0.5 mg/minute) of PGF2alpha, blood PGF plateaued at 29.5 ng/ml with a metabolic clearance rate of 17.0 liters per minute.

Plasma prolactin, growth hormone, luteinizing hormone and glucocorticoids after prostaglandin F2alpha in heifers.

Summary Blood plasma PRL, GH and glucocorticoids in heifers increased severalfold within 5-15 min after im injections of 15, 30, or 60 mg PGF2α or after a single 5 mg iv injection of PGF2α. Plasma LH increased at least twofold over basal estimates but not until 1.5-6 hr after im PGF2α. Constant iv infusion of PGF2α at the rate of 0.5 mg/min for 30 min produced greater plasma concentrations of PRL, GH, glucocorticoids and LH than those found after im injections. Plasma glucose increased 59-67% above pretreatment values between 30 and 60 min after iv administration of PGF2α. Plasma insulin increased more than twofold over basal estimates at 45 min after PGF2α administration, but these increases only approached significance (P ≃ 0.10). Free fatty acids did not change significantly (P > 0.05) after PGF2α administration. While exogenous PGF2α administration causes marked increases in several plasma hormones and glucose, the mechanism of action is unclear.

Androgens in the Bovine Fetus and Dam

Summary Umbilical arterial and venous blood, and fetal testes were taken from 38 bovine fetuses at 90, 180 or 260 days of gestation. Concurrently blood also was taken from the jugular, and from the uterine artery and vein of the dams. Testosterone and androstenedione were determined by radioimmunoassays. Fetal testicular homog-enates had 0.96 and 0.35 μg/g of testosterone and 0.39 and 0.50 μg/g of androstenedione at 180 and 260 days of gestation, respectively. Males had five to tenfold more serum testosterone and about twofold more androstenedione than female fetuses at each trimester of gestation. Male fetal blood testosterone decreased (P < 0.01) from 2.7 to 0.3 ng/ml between 90 and 260 days of gestation. But, maternal testosterone and androstenedione increased (P < 0.05) during gestation in cows with males, but not in cows with female fetuses. Testosterone was higher (P < 0.05) in cows carrying males than in cows with female fetuses. Androstenedione was higher in blood leaving the placenta on both the maternal and on the fetal sides suggesting placental synthesis of androstenedione.

Estrus, ovulation, progesterone and luteinizing hormone after prostaglandin F2a in mares.

Summary After a control estrous cycle, 10 mg PGF2α was deposited in the uterus in six mares (300-500 kg; 3-20 yr) at 7-9 days after ovulation. Blood plasma progesterone fell from 13.6 to 5.8 ng/ml within 12 hr and to 0.9 ng/ml at 48 hr after PGF2α, estrus began in 2.2 days and ovulation occurred at Day 5.8 of estrus. The estrus after PGF2α persisted longer than estrus in control cycles (7.5 vs 5.2 days; P < 0.05), but the interval from ovulation to the end of estrus was unchanged (1.6 vs 1.5 days). An increase in blood plasma LH began the day before estrus and continued past ovulation; LH declined beginning 2 days after ovulation and continuously for 8 days. A control estrous cycle after the PGF2α cycle resembled in every measurement the control cycle before PGF2α, indicating no carry-over effect of PGF2α. Subcutaneous injection of 15 mg PGF2α 7-9 days after ovulation also caused luteolysis, estrus, and ovulation — resembling in every detail the comparable events after intrauterine PGF2α. We conclude that PGF2α given sub-cutaneously or into the uterus is a powerful luteolysin with no carry-over effect on subsequent control estrous cycles in mares.

Semen Output of Rabbits Ejaculated After Varying Sexual Preparation.

Summary Three intensities of sexual preparation were compared with none using 9 rabbits which each furnished 2 ejaculations every second day for 38 days. The average sperm content of first ejaculations after one false mount (102.9 × 106) was 178% greater than that following no sexual preparation (37.0 × 106) and 3 false mounts resulted in an additional 40% increment in sperm output over one false mount. Sexual preparation also increased average sperm content of second ejaculations, although the increments were not as large as those obtained in first ejaculations. Analyses of seminal volume and total fructose content revealed that sexual preparation stimuli also affected accessory glands, but the magnitude of effect was proportionately smaller than the magnitude of the effect on epididymides. Sexual preparation also reduced the relative magnitude of the within-buck variance of total sperm output.

Release of Bovine Luteinizing Hormone by Purified Porcine and Synthetic Gonadotropin Releasing Hormone

Summary LH concentration in serum of heifers averaged 0.5 ng/ml and increased to peaks of 1.9, 7.3 and 11.1 ng/ml after a single iv injection of 5, 20 or 80 μg GnRH, respectively. Similarly, LH concentration in serum from mature bulls averaged 1.1 ng/ml before GnRH and increased to peaks of 9.2, 19.3 and 39.1 ng/ml after 10, 40 and 160 μg GnRH, respectively. The interval from GnRH to the LH peak and magnitude of the peak were positively correlated. Exposure of pituitary explants, in constant superfusion, to 1 or 4 ng GnRH increased LH release from a pre-treatment base line of 0.25 ng/mg/min to 0.94 and 1.50 ng/mg/min after 20 min, respectively. LH release did not return to base line by 40 min after exposure to GnRH. A comparison of purified porcine and synthetic GnRH revealed parallel increases in media LH concentration with time after GnRH.