Angiotensin acts at the subfornical organ to increase plasma oxytocin concentrations in the rat

We have examined the effects of systemic angiotensin II (AII) on plasma oxytocin (OXY) concentrations in freely moving male Sprague-Dawley rats. We have also examined the role of the subfornical organ (SFO) as a CNS site at which circulating AII acts to influence secretion of this neurohypophysial peptide. OXY concentrations were measured by radioimmunoassay in plasma samples obtained by drawing blood samples through indwelling atrial catheters. In SFO intact animals (n = 8) AII infusion (1.0 microgram/kg/min) resulted in increases in plasma OXY concentrations from baseline values of 6.8 +/- 2.5 pg/ml to postinfusion concentrations of 44.9 +/- 11.9 pg/ml. In a second series of experiments electrolytic lesions were placed in the region of the SFO prior to testing the effects of AII infusion on OXY concentrations. Two further experimental groups were thus established according to the histologically verified location of lesions in either the rostral or caudal SFO. In the caudal SFO lesioned group AII infusion resulted in increases in plasma OXY concentrations from control values of 6.9 +/- 1.4 pg/ml to postinfusion levels of 45.1 +/- 9.8 pg/ml. These changes were not significantly different from the SFO intact group. In contrast rostral SFO lesions resulted in significantly elevated basal concentrations of OXY (17.4 +/- 3.4 pg/ml, n = 6) while postinfusion concentrations were found to be 22.8 +/- 4.9 pg/ml indicating that AII infusion was without effect following such lesions. These data are in accordance with the hypothesis that circulating AII acts at the SFO to influence SFO efferents which in turn activate OXY secreting neurons in the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei. These neuroendocrine cells then release this peptide into the systemic circulation from the posterior pituitary.     

Oxytocin infusion from day 10 after oestrus extends the luteal phase in non-pregnant cattle

Oestrus was synchronized in 8 cyclic heifers by progesterone treatment (PRID), after which the animals were monitored for one control cycle to measure the inter-oestrous interval. Osmotic minipumps containing saline (controls, N = 3) or oxytocin (N = 5) were implanted subcutaneously on Day 10 of the second cycle, and removed 12 days later. Jugular venous blood samples were collected daily for measurement of progesterone, and every 2 days for oxytocin. In addition, blood samples were taken every 10 min from 1 h before to 3 h after minipump insertion for measurement of plasma 15-keto-13,14-dihydroprostaglandin-F-2 alpha (PGFM) and every 30 min over the same period for measurement of progesterone and oxytocin. The lengths of the first untreated cycle in both groups of heifers were 20.2 +/- 0.56 (mean +/- s.e.m.) days compared with 25.4 +/- 0.81 days after oxytocin treatment (P less than 0.001). Oxytocin plasma concentrations in treated animals rose from less than 10 pg/ml to 70-500 pg/ml by 2 h after the start of oxytocin infusion and remained elevated until treatment was withdrawn. There was no increase in PGFM concentrations immediately after minipump insertion. Plasma progesterone concentrations were similar in treated and control animals but remained at mid-luteal levels for an average of 5 days longer in treated heifers. It is concluded that continuous administration of oxytocin can extend the luteal life-span in cattle.     

Secretion patterns of oxytocin and PGF2alpha-metabolite in response to cervical dilatation in cyclic mares

We conducted the present study to establish a standardized method for cervical stimulation without affecting the endometrium, and to investigate the effect on estrous cycle pattern and concentrations of progesterone, oxytocin and PGF2alpha-metabolite of cervical dilatation in the mare. Six healthy Haflinger mares underwent three different treatments (control, insertion, dilatation) on Days 5 and 7 of the cycles in different orders according to a Latin square design. During dilatation, the balloon of the catheter was inflated stepwise every 30s with warm physiological saline to a maximum of 50 ml. At this stage the size of the balloon was 4.5 cm in diameter and 6 cm length. Estrous cycle length was significantly shortened by dilatation when compared to controls (control: 22.8+/-1.7, insertion: 21.8+/-2.5, dilatation: 20.0+/-1.3 days; P<0.05). Concentrations of progesterone at Days 10, 12 and 14 after ovulation were significantly lower in dilatation cycles. Calculation of the area under the curve (AUC) for progesterone secretion from Day 7 to Day 12 also revealed a significant decrease in progesterone secretion in the dilatation group (dilatation: 34.1+/-7.3, insertion: 35.6+/-7.8, control: 39.1+/-5.9 ng/ml; P<0.05). Cervical insertion and dilatation caused a rapid and pronounced increase in plasma concentrations of oxytocin from basal levels (1.0-6.1 pg/ml) to maximum peaks (insertion: 125.5 pg/ml and dilatation: 305.2 pg/ml). The AUC for oxytocin was significantly higher after insertion (Day 5: 858.4+/-469.9; Day 7: 411.9+/-213 pg/ml/h) and dilatation (Day 5: 1697+/-1725; Day 7: 1078.5+/-764 pg/ml/h) when compared to controls (Day 5: 186+/-98; Day 7: 156+/-23.5 pg/ml/h; P<0.05). Manipulations did not cause considerable changes in plasma PGF2alpha-metabolite concentrations. Because cervical dilatation up to a diameter of 4.5 cm did not cause any immediate PGF2alpha release, the luteolytic pathway is unlikely to be responsible for shortening the length of diestrus and the estrous cycle. The present data suggest an involvement of oxytocin in the shortening of the luteal phase in response to cervical manipulation.     

Pulsatile release of oxytocin into the circulation of the ewe during oestrus, mating and the early luteal phase

Two experiments were designed to investigate release patterns of oxytocin into plasma during oestrus and the early luteal phase. In Exp. 1, blood samples were collected from 5 ewes every 30 min for 10 h during 6 days around oestrus and the early luteal phase. During oestrus concentrations of oxytocin were generally low (1.27 +/- 0.54 pg/ml; mean +/- s.d.) but with occasional pulses up to 6 pg/ml. By Day 5 mean basal concentrations had risen to 4.5 +/- 2.1 pg/ml with a fluctuating release pattern. In Exp. 2, a method was developed for continuous blood sampling from conscious, unrestrained ewes. On the predicted day of oestrus following an untreated oestrous cycle, 8-ml blood samples were collected every minute for two 35-min periods (8 ewes: 16 sampling periods). For 6 ewes a ram was introduced to the pen for part of this time, and resulting behaviour was recorded. Additional blood samples were assayed for LH and progesterone to determine the stage of the cycle. Overall mean oxytocin concentrations ranged from 1.5 +/- 0.53 to 6.8 +/- 5.25 pg/ml in different animals. Ewes which were both in oestrus and exposed to the ram showed a pulsatile oxytocin release pattern consisting of low baseline concentrations with short-duration pulses superimposed (duration 1-4 min; amplitude 2.5-31.7 pg/ml; frequency 3.18/h). Coitus was not temporally associated with pulsatile release. However, the importance of the presence of the ram was indicated by total separation of 2 oestrous ewes from the ram until after experimentation. In these animals only 1 pulse of oxytocin was detected in 2.7 h of sampling. It is concluded that, although mean oxytocin concentrations at oestrus were low, short duration pulses were released into the plasma at this time. This effect may be dependent on the presence of a ram.     

Plasma oxytocin concentrations during late pregnancy and parturition in the dog

While oxytocin is widely used in the treatment of dystocia in dogs, there is little information about its secretion before and during normal unassisted whelping. We therefore measured plasma oxytocin concentrations during late pregnancy and the expulsive stage of parturition. Blood samples were collected from eight dogs at 3-min intervals during a 42-min period between the 2nd and 14th day before whelping and during parturition after the birth of 1-3 pups. The litters consisted of 5-15 pups and the progression of the expulsive stage was linear and nearly parallel in the eight bitches. The overall mean (+/-S.D.) plasma oxytocin concentration during late pregnancy was 3.6+/-2.1pg/ml. Mean values in individual dogs ranged from 1.2 to 7.4 pg/ml, but the intra-animal variation was rather small. During the expulsive stage the overall mean (+/-S.D.) plasma oxytocin concentration was 12.9+/-13.9 pg/ml, with mean values in individual dogs ranging from 3.5 to 46 pg/ml. The mean area under the oxytocin curve for parturient dogs was significantly higher (P<0.05) than for pregnant dogs. During the expulsive stage, the peak plasma oxytocin level in individual dogs ranged between 10 and 117 pg/ml. In six of the eight dogs a pup was born during blood collection and in five of these animals the plasma oxytocin concentration increased temporarily during periods of abdominal straining and expulsion. However, straining efforts and expulsion were not consistently associated with a rise in the circulating oxytocin level. It is concluded that in the dog plasma oxytocin levels are higher and more variable during the expulsive stage of parturition than during late pregnancy. Interrelationships between the secretion pattern of oxytocin, the level of uterine contractility, and the progress of fetal expulsion in dogs need further exploration.     

Oxytocin and bovine parturition: a steep rise in endometrial oxytocin receptors precedes onset of labor.

Oxytocin receptors were measured in myometrium and intercaruncular endometrium of cows during pregnancy and parturition. Concentrations of estradiol-17 beta, estrone, and progesterone in peripheral blood were also measured. Receptor concentrations in the endometrium rose almost 200-fold from Day 20 to term (p < 0.0001, ANOVA), from 40 +/- 11 to 7300 +/- 1430 fmol/mg protein. Myometrial receptor concentrations increased 10-fold from 180 +/- 36 fmol/mg on Day 20 to 1850 +/- 360 fmol/mg protein at term (p < 0.0001, ANOVA). During labor, endometrial receptors (6600 +/- 1300 fmol/mg) remained at prelabor values, whereas myometrial receptor concentrations had decreased to 1190 +/- 316 fmol/mg (not significant) and declined further postpartum. Plasma concentrations of progesterone declined from 4-5 ng/ml to about 2 ng/ml between Days 250 and 282 and dropped to < 0.2 ng/ml shortly before delivery. Plasma concentrations of estrone and estradiol-17 beta were below 10-20 pg/ml until Day 230. Estrone concentrations were significantly (p < 0.05) increased by Day 250 and estradiol-17 beta by Day 270, and then both rose rapidly. During labor, plasma estrone was 1135 +/- 245 pg/ml and plasma estradiol-17 beta was 226 +/- 131 pg/ml. The molar ratio of estrone and estradiol-17 beta to progesterone rose from less than 0.01 to 4.4 during labor, and was correlated with oxytocin receptor concentrations in endometrium (r = 0.5160, p < 0.001), but not those in myometrium (r = 0.0122). The regulation of oxytocin receptors by ovarian hormones in the two tissues may therefore differ.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of intra-ovarian infusion of oxytocin on plasma progesterone concentrations in pregnant ewes.

The function of oxytocin receptors in the corpus luteum of pregnant ewes was investigated by infusing saline or oxytocin (100 ng/min) into the utero-ovarian artery of pregnant ewes (62 +/- 5 days, n = 12). During a 4-h infusion, plasma oxytocin (OT) concentration increased to 268 +/- 80 pg OT/ml in the OT-infused group and remained unchanged at 2.5 +/- 1.5 pg OT/ml in the saline-infused group. Progesterone concentration in jugular venous plasma (17 +/- 9 ng/ml) rapidly decreased during oxytocin infusion to 59 +/- 10% and 26 +/- 9% of control at 1.5 and 2 h, respectively; the utero-ovarian venous concentration of 64 +/- 38 ng/ml decreased by a similar magnitude during oxytocin infusion. Electron microscopy of corpora lutea, removed at the end of the experiments, showed no indication of luteolytic changes following oxytocin infusion. It was concluded that oxytocin markedly and rapidly reduces progesterone secretion in pregnant ewes.     

Hormonal changes during luteal regression in farmed fallow deer, Dama dama

Concentrations of progesterone, oxytocin and PGFM (pulmonary metabolite of PGF-2 alpha) were measured in plasma from peripheral blood samples collected from 5 fallow does every hour or 2 h for 12-h periods on Days 15-20 inclusive of the oestrous cycle (i.e. luteolysis). For 3 does that exhibited oestrus on Day 21, plasma progesterone concentrations fluctuated between 3 and 10 ng/ml on Days 15-18 inclusive. Thereafter, values declined progressively to attain minimum concentrations of less than 0.05 ng/ml on Day 20. Basal concentrations of plasma oxytocin and PGFM fluctuated between 5 and 20 pg/ml and 10 and 100 pg/ml respectively. Episodic pulses of plasma oxytocin (greater than 300 pg/ml) occurred on Days 15 and 16, whereas pulses of plasma PGFM (greater than 400 pg/ml) occurred on Days 19 and 20. There was little apparent correlation between episodic pulses of the two hormones. For 2 does that exhibited oestrus on Day 22, plasma progesterone concentrations declined to minimum values of 1.0-1.5 ng/ml by Day 20. One of these does showed very high levels of oxytocin secretion throughout the sampling period while the other showed an apparent paucity of oxytocin secretory periods. Two does hysterectomized on Day 13 of their second oestrous cycle failed to exhibit further oestrous cycles. Continual elevation of plasma progesterone concentrations (2-6 ng/ml) for an 8-month period indicated persistence of the corpus luteum after hysterectomy. It is concluded that luteolysis in fallow deer involves episodic secretion of both oxytocin and PGF-2 alpha.     

The role of sub-optimal preovulatory oestradiol secretion in the aetiology of premature luteolysis during the short oestrous cycle in the cow

Premature regression of the corpus luteum, following the first post partum ovulation, is often preceded by sub-optimal preovulatory oestradiol secretion and accompanied by elevated levels of oxytocin receptors early in the luteal phase. We have investigated the role of preovulatory oestradiol in the control of subsequent oxytocin receptor concentration and activity by treating ovariectomised cows, over a simulated 48 h follicular phase, with high (600 microg per day) medium (300 microg per day) or low (150 microg per day) levels of oestradiol. These doses of oestradiol generated mean+/-S.E.M. plasma oestradiol concentrations of 12.1+/-1.0, 4.9+/-0.5 and 2.9+/-0.4 pg ml(-1), respectively. In Study 1 (n=4 per group), we found that by day 4 following oestrus there was a significant (P< 0.05) effect of the level of oestradiol on the inhibition of oxytocin binding activity measured in endometrial biopsy samples. This had fallen to mean+/-S.E.M. concentrations of 25+/-2 fmol per mg protein in the high group, 47+/-8 fmol per mg protein in the medium group and 65+/-12 fmol per mg protein in the low group. In Study 2, cows (n=3 per group) were treated with the same three levels of oestradiol followed by treatment with increasing levels of progesterone from days 3 to 6 following oestrus, generating mean+/-S.E.M. plasma concentrations of 2.17+/-0.18 ng ml(-1) by day 6. On day 6, there was a significant (P< 0.01) effect of the level of oestradiol on PGF(2alpha) release in response to oxytocin challenge. High, medium and low oestradiol groups exhibiting mean+/-S.E.M., increase plasma PGF(2alpha) metabolite concentrations of 10.0+/-2.2, 21.3+/-4.3 and 41.3+/-1.2 pg ml(-1), respectively, during the hour after oxytocin administration. From these results, we postulate that at the first post partum ovulation a low level of preovulatory oestradiol can result in the early generation of a luteolytic mechanism during the subsequent luteal phase due to impaired inhibition of oxytocin receptors allowing increased PGF(2alpha) release.     

Extension of oestrous cycles and prolonged secretion of progesterone in non-pregnant cattle infused continuously with oxytocin

The experimental objective was to evaluate how continuous infusion of oxytocin during the anticipated period of luteolysis in cattle would influence secretion of progesterone, oestradiol and 13,14-dihydro-15-keto-prostaglandin F-2 alpha (PGFM). In Exp. I, 6 non-lactating Holstein cows were infused with saline or oxytocin (20 IU/h, i.v.) from Day 13 to Day 20 of an oestrous cycle in a cross-over experimental design (Day 0 = oestrus). During saline cycles, concentrations of progesterone decreased from 11.0 +/- 2.0 ng/ml on Day 14 to 2.0 +/- 1.3 ng/ml on Day 23; however, during oxytocin cycles, luteolysis was delayed and progesterone secretion remained near 11 ng/ml until after Day 22 (P less than 0.05). Interoestrous interval was 1.6 days longer in oxytocin than in saline cycles (P = 0.07). Baseline PGFM and amplitude and frequency of PGFM peaks in blood samples collected hourly on Day 18 did not differ between saline and oxytocin cycles. In Exp. II, 7 non-lactating Holstein cows were infused with saline or oxytocin from Day 13 to Day 25 after oestrus in a cross-over experimental design. Secretion of progesterone decreased from 6.8 +/- 0.7 ng/ml on Day 16 to less than 2 ng/ml on Day 22 of saline cycles; however, during oxytocin cycles, luteolysis did not occur until after Day 25 (P less than 0.05). Interoestrous interval was 5.9 days longer for oxytocin than for saline cycles (P less than 0.05). In blood samples taken every 2 h from Day 17 to Day 23, PGFM peak amplitude was higher (P less than 0.05) in saline (142.1 +/- 25.1 pg/ml) than in oxytocin cycles (109.8 +/- 15.2 pg/ml). Nevertheless, pulsatile secretion of PGFM was detected during 6 of 7 oxytocin cycles. In both experiments, the anticipated rise in serum oestradiol concentrations before oestrus, around Days 18-20, was observed during saline cycles, but during oxytocin cycles, concentrations of oestradiol remained at basal levels until after oxytocin infusion was discontinued. We concluded that continuous infusion of oxytocin caused extended oestrous cycles, prolonged the secretion of progesterone, and reduced the amplitude of PGFM pulses. Moreover, when oxytocin was infused, pulsatile secretion of PGFM was not abolished, but oestrogen secretion did not increase until oxytocin infusion stopped.     

Interactions between oxytocin, glucagon and glucose in normal and streptozotocin-induced diabetic rats

Oxytocin has been suggested to have glucoregulatory functions in rats, man and other mammals. The hyperglycemic actions of oxytocin are believed to be mediated indirectly through changes in pancreatic function. The present study examined the interaction between glucose and oxytocin in normal and streptozotocin (STZ)-induced diabetic rats, under basal conditions and after injections of oxytocin. Plasma glucose and endogenous oxytocin levels were significantly correlated in cannulated lactating rats (r = 0.44, P less than 0.01). To test the hypothesis that oxytocin was acting to elevate plasma glucose, adult male rats were injected with 10 micrograms/kg oxytocin and killed 60 min later. Oxytocin increased plasma glucose from 6.1 +/- 0.1 to 6.8 +/- 0.2 mM (P less than 0.05), and glucagon from 179 +/- 12 to 259 +/- 32 pg/ml (P less than 0.01, n = 18). There was no significant effect of oxytocin on plasma insulin, although the levels were increased by 30%. A lower dose (1 microgram/kg) of oxytocin had no significant effect on plasma glucose or glucagon. To eliminate putative local inhibitory effects of insulin on glucagon secretion, male rats were made diabetic by i.p. injection of 100 mg/kg STZ, which increased glucose to greater than 18 mM and glucagon to 249 +/- 25 pg/ml (P less than 0.05). In these rats, 10 micrograms/kg oxytocin failed to further increase plasma glucose, but caused a much greater increase in glucagon (to 828 +/- 248 pg/ml) and also increased plasma ACTH. A specific oxytocin analog, Thr4,Gly7-oxytocin, mimicked the effect of oxytocin on glucagon secretion in diabetic rats. The lower dose of oxytocin also increased glucagon levels (to 1300 +/- 250 pg/ml), but the effect was not significant. A 3 h i.v. infusion of 1 nmol/kg per h oxytocin in conscious male rats significantly increased glucagon levels by 30 min in normal and STZ-rats; levels returned to baseline by 30 min after stopping the infusion. Plasma glucose increased in the normal, but not STZ-rats. The relative magnitude of the increase in glucagon was identical for normal and diabetic rats, but the absolute levels of glucagon during the infusion were twice as high in the diabetics. To test whether hypoglycemia could elevate plasma levels of oxytocin, male rats were injected i.p. with insulin and killed from 15-180 min later. Plasma glucose levels dropped to less than 2.5 mM by 15 min. Oxytocin levels increased by 150-200% at 30 min; however, the effect was not statistically significant.(ABSTRACT TRUNCATED AT 400 WORDS)     

Oxytocin plasma level in the lactating sows--effect of suckling

Oxytocin concentration in the peripheral blood was measured by RIA during suckling period in lactating sows (n = 8). Blood samples were taken from the jugular vein around the clock for every 2 h on day 5, 10, 15, 20, 25, 30 and on day 35 of lactation. Besides that blood samples were collected more frequently during suckling periods. Oxytocin plasma concentration was very low and in most cases it was on a border of sensitivity of our method (3 pg/ml). Marked but short-lasting rise of oxytocin was observed only during a period of initial massage of the udders by the piglets. This rise observed in all studied pigs was higher (p less than 0.01) compared to the values before the massage on the onset of lactation only, and was 14.6 +/- 4.2 pg/ml and 6.4 +/- 1.2 pg/ml on day 5 and day 10 of lactation, respectively. In all other studied days in a few cases only suckling stimulated the release of oxytocin over its basic concentration. Mean values (+/- SEM) of oxytocin in blood samples collected during massage of udder on day 15, 20, 25, 30 and day 35 were 3.7 +/- 0.5, 4.2 +/- 0.8, 4.9 +/- 1.1, 3.2 +/- 0.4 and 3.0 +/- 0.6 pg/ml plasma, respectively. There was no relationship between the size of the litters and neither basic level of oxytocin nor its blood concentration during suckling (r = 0.13).     

Application of sensitive enzymeimmunoassays for oxytocin and prolactin determination in blood plasma of yaks (Poephagus grunniens L.) during milk let down and cyclicity

Highly sensitive and specific enzymeimmunoassays for oxytocin and prolactin determination in yak plasma using the biotin-streptavidin amplification system and the second antibody coating technique were validated and applied for determining their profiles during milk let down and cyclicity in yaks. Oxytocin EIA was conducted taking duplicate 200 microl of unknown plasma samples and standards per well. The lowest detection limit was 0.2 pg/well, which corresponded to 1pg/ml plasma. Prolactin EIA was carried out directly in 50 microl of yak plasma. The sensitivity of EIA procedure was 5 pg/well prolactin, which corresponded to 0.1 ng/ml plasma. Mean plasma prolactin concentrations although high at estrus were not statistically different (P > 0.05) from the hormone concentrations on other days. Mean plasma prolactin concentrations during non-breeding season were significantly higher (P < 0.001) than that recorded in breeding season. Oxytocin and prolactin profiles were also obtained in two yaks before, during and after milking. A sharp release of oxytocin and prolactin shortly after udder stimulation was observed. High levels of oxytocin and prolactin were maintained during milking, falling sharply thereafter.     

Plasma oxytocin concentrations in cyclic mares and sexually aroused stallions

An experiment was conducted to measure plasma oxytocin concentrations at 4 different stages of the estrous cycle in 11 pony mares. Plasma oxytocin concentrations (muU/ml +/- SE) were found to be higher (P<.01) on day 2 of estrous (39.8 +/- 12.5) and day 5 post-ovulation (33.1 +/- 12.0) than on day 10 (2.3 +/- 1.6) and day 15 post-ovulation (6.8 +/- 4.1). A second experiment was conducted to measure jugular plasma oxytocin concentrations before and after sexual arousal in six pony stallions. Oxytocin concentrations (muU/ml +/- SE) were higher (P<0.06) after sexual arousal (50.5 +/- 8.9) than before sexual arousal (23.8 +/- 2.9). These data suggest plasma oxytocin concentrations may be associated with ovarian function in mares and with sexual behavior in stallions.     

Oxytocin in the cerebrospinal fluid and plasma of pregnant and nonpregnant subjects

The oxytocin concentration in the cerebrospinal fluid (CSF) and plasma of pregnant women at term with and without labor pain were measured by radioimmunoassay and compared with those of non-pregnant women of matched age. The oxytocin concentrations in the CSF were 4.9 +/- 4.1 microU/ml (mean +/- S.D.) in pregnant women with labor pain, 4.1 +/- 2.4 microU/ml in those without labor pain and 4.0 +/- 2.8 microU/ml in nonpregnant women, and the oxytocin concentrations in the plasma of these subjects were 45.2 +/- 19.6, 17.1 +/- 22.2 and 7.0 +/- 5.3 microU/ml, respectively. Thus the oxytocin level in the CSF did not change appreciably even when the level in the plasma was raised in the pregnant women with labor pain. These findings suggest that oxytocin does not penetrate the blood-brain barrier, and that oxytocin in the CFS has little or no central role in parturition in women.     

Alteration of oestrous cycle length, ovarian function and oxytocin-induced release of prostaglandin F-2 alpha by intrauterine and intramuscular administration of recombinant bovine interferon-alpha to cows.

An experiment was conducted to (i) determine whether administration of recombinant bovine interferon-alpha I1 (rBoIFN-alpha) attenuates oxytocin-induced release of prostaglandin F-2 alpha and (ii) confirm previous observations that rBoIFN-alpha causes acute changes in body temperature and circulating concentrations of progesterone. Cows were treated twice a day from Day 14 to Day 17 after oestrus with a control regimen (bovine serum albumin (BSA), i.m. + BSA intrauterine (i.u.)), rBoIFN-alpha, i.u. + BSA, i.m. (rBoIFN-IU) or rBoIFN-alpha, i.m. + BSA, i.u. (rBoIFN-IM). On Day 17, plasma concentrations of 13,14-dihydro,15-keto-prostaglandin F-2 alpha (PGFM) were measured after injection of oxytocin. Cows treated with rBoIFN-IU and rBoIFN-IM had longer oestrous cycles and luteal lifespans than control cows. A hyperthermic response and decline in plasma concentrations of progesterone was noticed after administration of rBoIFN-alpha on Day 14. On other days, the hyperthermic response was not present and the decline in progesterone was less pronounced. There was no significant effect of rBoIFN-alpha on circulating concentrations of oestradiol between Days 14 and 17. The release of PGFM induced by oxytocin was lower in cows treated with rBoIFN-alpha than in control cows. Oxytocin caused increased plasma concentrations of PGFM in four of five control cows, two of five rBoIFN-IU cows and two of five rBoIFN-IM cows. The peak PGF-2 alpha response to oxytocin (peak value after injection minus mean concentration before injection) was 257.8 +/- 61.3 pg/ml for control cows, 100.7 +/- 40.8 pg/ml for rBoIFN-IU and 124.9 +/- 40.4 pg/ml for rBoIFN-IM. It is concluded that rBoIFN-alpha can reduce oxytocin-induced PGFM release and may therefore extend the lifespan of the corpus luteum by interfering with events leading to luteolytic release of PGF from the uterus. Administration of rBoIFN-alpha can cause acute changes in body temperature and circulating concentrations of progesterone that become less severe after repeated exposure to rBoIFN-alpha.     

Possible involvement of endogenous beta-endorphin in the pathophysiological mechanisms of Pichinde virus-infected guinea pigs.

Previously, we demonstrated that naloxone, an opiate antagonist, prolonged survival of strain 13 guinea pigs infected with Pichinde virus. Thus, endogenous opiates may be involved in the pathogenesis of this viral disease. To determine whether endogenous opiate levels were affected by Pichinde viral infection, beta-endorphin concentrations in plasma and cerebrospinal fluid (CSF) of normal and infected strain 13 guinea pigs were measured by radioimmunoassay. Cerebrospinal fluid beta-endorphin concentrations were 78.0 +/- 13.2 pg/ml on postinoculation day (PID) 7, 59.0 +/- 5.6 pg/ml on PID 12, and 58.8 +/- 5.4 pg/ml on PID 14. These values were significantly higher than baseline levels of CSF beta-endorphin: 30.8 +/- 1.9 pg/ml. Plasma beta-endorphin concentrations of infected animals increased significantly to 202.1 +/- 17.9 pg/ml on PID 7 and to 154.2 +/- 21.4 pg/ml on PID 12 from a mean baseline value of 84.2 +/- 13.1 pg/ml. After a primer intravenous injection of beta-endorphin (10, 15, or 30 micrograms/kg), followed by constant infusion of beta-endorphin (15, 45, or 90 micrograms/kg.hr) to control noninfected guinea pigs, heart rate (except with the lowest dose) and mean blood pressure decreased markedly. Under these experimental conditions, concentrations of plasma and CSF beta-endorphin increased simultaneously with different magnitude. Because both Pichinde viral infection and beta-endorphin administration produced a similar trend of cardiovascular disturbances, leading to hypotension and bradycardia, increased concentrations of plasma and CSF beta-endorphin may play a partial role in the pathophysiological mechanisms of Pichinde virus infection.     

Aminopropionic acid receptors in paraventricular nucleus mediate pressor and vasopressin responses to endothelin-1 in subfornical organ

Endothelin-1 (ET-1) acts at selected brain loci to elicit a pressor response and secretion of vasopressin (AVP). Glutamatergic receptors of the N-methyl-D-aspartate (NMDA) subtype mediate ET-1-induced AVP secretion in vitro, but the role of glutamatergic receptors in the pressor response and the secretion of AVP in vivo has not been studied. We hypothesized that both the pressor response and AVP secretion in response to ET-1 microinjection into subfornical organ (SFO) would be suppressed by ionotropic glutamatergic receptor antagonists in the paraventricular nucleus (PVN). Sinoaortic denervated male Long Evans rats were equipped with intracerebral cannulae directed into the SFO and the magnocellular region of the PVN bilaterally. Experiments were performed 5 days later in conscious rats. Direct injection of 5 pmol ET-1 into the SFO resulted in a 20 +/- 3 mm Hg increase in mean arterial pressure (MAP) (+/- SE) and a 14.1 +/- 0.3 pg/ml increase in the mean plasma AVP level (+/- SE) (P < 0.001 vs. artificial CSF) that was blocked by selective ET(A) inhibition. Neither the pressor response nor the increase in plasma AVP in response to ET-1 was altered despite prior injection of the NMDA blocker diclozipine (5 microg, MK801) into PVN bilaterally. In contrast, bilateral PVN injection with 6-cyano-7-nitroquinoxaline-2,3-dione (40 nmol, CNQX) prevented the pressor response (MAP +/- SE, - 4 +/- 4 mm Hg) and also inhibited AVP secretion (mean AVP level +/- SE, 0.16 +/- 0.50 pg/ml) (P < 0.001 vs. vehicle in PVN after injection of ET-1 into SFO). These findings support the conclusion that both the pressor response and AVP secretion in response to ET-1 acting at the SFO are mediated by a non-NMDA, most likely an aminopropionic acid glutamatergic receptor within the PVN.     

A combined radioimmunoassay and immunocytochemical study of ovarian oxytocin production during the periovulatory period in the ewe

Corpora lutea and follicles were taken from the ovaries of 12 ewes at intervals from the start of luteolysis until 3 days after ovulation. RIA analysis of the tissue oxytocin content showed that luteal oxytocin concentrations declined during luteolysis to reach basal values at about the time of the next ovulation. Oxytocin was first measurable in the walls of 3 out of 6 preovulatory follicles during the LH surge, with a small increase in concentration to 26.1 +/- 6.6 pg/mg before ovulation, and a further increase in the young corpus luteum to concentrations exceeding 1 ng/mg 2-3 days later. After the LH surge, oxytocin was also found in the follicular fluid at a concentration of 3.4 +/- 0.3 ng/ml. Using immunocytochemical techniques, oxytocin and neurophysin were first detected in the follicle wall immediately before ovulation, and were localized in the granulosa cells. After ovulation the stained cells initially formed strands which appeared to break down to clusters and then to individual cells as the corpus luteum matured. The immunocytochemical picture also suggested that neurophysin immunoreactivity increased within a few hours of ovulation but that processing to oxytocin may be delayed. Measurements of circulating oxytocin concentrations revealed a pulsatile release pattern throughout the follicular phase with the height of the pulses decreasing from 25 +/- 5 pg/ml during luteolysis to a minimum of 11 +/- 2 pg/ml during the LH surge.     

Beta-endorphin-like and alpha-MSH-like immunoreactivities in human milk

We measured with radioimmunoassay the beta-endorphin-like and alpha-MSH-like immunoreactivities in milk and plasma of 8 lactating women. Mean beta-endorphin concentrations ( +/- SD) were 16.6 +/- 6.7 fmol/ml in milk and 9.9 +/- 4.1 fmol/ml in plasma. alpha-MSH concentrations (mean +/- SD) were 39.4 +/- 15.5 pg/ml in milk and 18.2 +/- 8.4 pg/ml in plasma. The concentrations of both peptides in milk were significantly (p less than 0.05) higher than in plasma. No significant correlation between milk and plasma concentrations of these peptides was found.