Osmolality and secretion of vasopressins during pregnancy in Meriones crassus]

Endocrine and renal parameters were measured in a desert rodent, Meriones crassus. In virgin females, the urine and plasma osmolality was 2018 +/- 136 and 325 +/- 3 mosm/kg (m +/- SEM), the level of circulating vasopressin, 162 +/- 22 pg/ml and the plasma renin activity 14.3 +/- 0.9 ng/ml per h. During pregnancy, the renin-angiotensin system was activated, and the plasma vasopressin values remained similar to those of virgin animals in spite of a lower blood plasma osmotic pressure. During this period, the regulation of the hydromineral balance was modified. These data suggest a lowering of the osmotic thresholds for vasopressin and possibly also for thirst during pregnancy in this desert rodent.     

Role of AVP in mediating the altered core temperature response to a simulated open field in pregnant rats.

Near the term of pregnancy, rats have an attenuated core temperature response on exposure to a novel environment (e.g., a simulated open field) compared with that observed early in pregnancy or in nonpregnant rats. The present experiments were carried out on 26 nonpregnant and 26 pregnant rats to test the hypothesis that arginine vasopressin, functioning as an endogenous antipyretic substance in the central nervous system, mediates this attenuated core temperature response. Exposure to a simulated open field after intracerebroventricular (ICV) vehicle produced a significant increase in core temperature in both nonpregnant and pregnant animals, the magnitude and duration of which were greater in the nonpregnant rats. In nonpregnant rats, exposure to a simulated open field after ICV vasopressin V(1)-receptor antagonist altered the pattern of the core temperature response but not the core temperature index compared with that observed on exposure to a simulated open field after ICV vehicle. In pregnant animals, ICV vasopressin V(1)-receptor antagonist did not alter the core temperature response to a simulated open field compared with that observed after ICV vehicle. Thus our data do not support the hypothesis that a pregnancy-related activation of arginine vasopressin attenuates the core temperature response to a simulated open field in rats near the term of pregnancy.     

The effect of progesterone on oxytocin-stimulated intracellular mobilization of Ca2+ and prostaglandin E2 and F2alpha secretion from porcine myometrial cells

Our past studies have shown that porcine myometrium produce prostaglandins (PG) during luteolysis and early pregnancy and that oxytocin (OT) and its receptor (OTr) support myometrial secretion of prostaglandins E2 and F2alpha (PGE2 and PGF2alpha) during luteolysis. This study investigates the role of intracellular Ca2+ [Ca2+]i as a mediator of OT effects on PG secretion from isolated myometrial cells in the presence or absence of progesterone (P4). Basal [Ca2+]i was similar in myometrial cells from cyclic and pregnant pigs (days 14-16). OT (10(-7)M) increased [Ca2+]i in myometrial cells of cyclic and pregnant pigs, although this effect was delayed in myometrium from pregnant females. After pre-incubation of the myocytes with P4 (10(-5)M) the influence of OT on [Ca2+]i)was delayed during luteolysis and inhibited during pregnancy. Myometrial cells in culture produce more PGE2 than PGF2alpha regardless of reproductive state of the female. OT (10(-7)M) increased PGE2 secretion after 6 and 12 h incubation for the tissue harvested during luteolysis and after 12 h incubation when myometrium from gravid females was used. In the presence of P4 (10(-5)M), the stimulatory effect of OT on PG secretion was diminished. In conclusion: (1) porcine myometrial cells in culture secrete PG preferentially during early pregnancy and produce more PGE2 than PGF2alpha, (2) OT controls myometrial PGF2alpha secretion during luteolysis, (3) release of [Ca2+]i is associated with the influence of OT on PG secretion, and (4) the effects of OT on PG secretion and Ca2+ accumulation are delayed by P4 during luteolysis and completely inhibited by P4 during pregnancy.     

Vascular hyperresponsiveness to adrenomedullin during pregnancy is associated with increased generation of cyclic nucleotides in rat mesenteric artery

Cardiovascular adaptation is a hallmark of pregnancy. Here we report on vascular hyperresponsiveness to an endogenous vasodilator, adrenomedullin (ADM), during pregnancy. Intravenous administration of ADM dose dependently decreased the mean arterial pressure, and the decrease was significantly greater in pregnant compared with nonpregnant rats without affecting the heart rate. In endothelium-intact mesenteric artery precontracted by ED70 concentration of norepinephrine, the potency and efficacy of ADM in causing the vasodilation of mesenteric arterial rings from pregnant rats are significantly higher compared with nonpregnant females at diestrus. The magnitude of inhibition of concentration-dependent response to ADM by the inhibition of either soluble guanylate cyclase or adenylate cyclase was greater in pregnant rats. Moreover, ADM-induced cyclic nucleotide generation, both cGMP and cAMP, in the mesenteric artery was elevated during pregnancy and was sensitive to the receptor antagonist, ADM22-52. These findings suggest that during pregnancy the vasodilatory effects of ADM are greater and are associated with increased generation of cyclic nucleotides in resistance vessels, and these changes may be part of the cardiovascular adaptations that occur during pregnancy.     

Sex steroid hormone binding globulin levels and free 17 beta-estradiol and testosterone in cynomolgus monkeys during different reproductive states

The effect of differences in sex hormone binding globulin (SHBG) levels associated with reproductive status on free 17 beta-estradiol (E2) and testosterone (T) was characterized in cynomolgus monkeys. Cycling female cynomolgus monkeys had higher SHBG levels than males, pregnant and lactating females (P less than 0.05). Ovariectomized females were not different than control females, suggesting no hypoestrogenic effect. The percentage of free T was elevated in pregnant animals (P less than 0.05) compared to normal males and females, but the percentage of free E2 was similar between these groups. Although a gender difference in the percentages of free E2 and T was not detected, there was a gender difference in the free T and E2 concentrations due to endogenous secretion. Increased free E2 concentrations during pregnancy were the result of endogenous secretion rather than the decreased binding capacity of SHBG; the increased percentage of free T during pregnancy significantly increased free T concentrations. These data suggest that the gender difference in SHBG levels in cynomolgus monkeys is due to androgenic influences and that estrogens have minimal influence. Furthermore, the decrease in SHBG levels during pregnancy and lactation may not be entirely dependent on these androgenic influences.     

Level of energy intake affects the estrous cycle in Sundevall's jird (Meriones crassus)

Effects of energy intake on the estrous cycle of the desert gerbillid, Sundevall's jird (Meriones crassus; 80 g; n=22) were studied. Females were offered either maintenance or below maintenance levels of millet seeds and ad lib. Atriplex halimus leaves and stems; drinking water was not available. Vaginal smears were used to determine sexual stage. We hypothesized that the estrous cycle ceases at low levels of energy intake and commences when sufficient energy is available. Females lost body mass linearly with a decrease in metabolizable energy intake. Estrous cycle averaged 4.46 d at maintenance energy intake but increased to an average of 7.81 d at 70% of maintenance energy intake. A cessation of the cycle occurred at an energy intake below 70% of maintenance requirements, which resulted in a body mass loss of more than 1% per day. More variability in the length of the different stages of the cycle was found with lower levels of energy intake. When offered ad lib. millet seeds and A. halimus (n=14), recovery to the normal cycle was attained within 10 d by 43% of the females and within 16 d by the rest of the females. Recovery time was longest in females that previously had the lowest energy intake. We concluded that the estrous cycle of M. crassus is sensitive to energy intake. With restricted energy intake, the estrous cycle and reproductive activities cease but can be restored with provision of adequate energy. This strategy ensures that reproduction occurs when conditions of food availability and body condition of the females are favorable.     

Effects of biological traits on capture-induced parturition in a freshwater stingray and perspectives for species management

Elasmobranchs are particularly vulnerable to overexploitation and population depletion, especially due to their life-history traits, such as low reproductive output and slow growth. Given that capture-induced parturition (abortion or premature birth) is a common consequence of fisheries in elasmobranchs, but still little studied, we investigated how the abortion/premature birth process varies in response to reproductive traits in a freshwater stingray, Potamotrygon amandae. Our results revealed that capture-induced parturition was affected by reproductive traits, such as litter size (one to seven) and gestation stage. The event occurred faster in pregnant females with high litter size during late pregnancy. Also, as found in other elasmobranchs, litter size was positively correlated with maternal size. These findings indicate that larger pregnant females in late pregnancy are more vulnerable to capture-induced parturition. This study improves our understanding of the capture-induced parturition process in stingrays, and provides useful information for management strategies and future recommendations for elasmobranch conservation.     

Pregnancy influence on the vascular interactions between nitric oxide and other endothelium-derived mediators in rat kidney

Peripheral vascular resistance and sensitivity to circulating pressor and vasoconstrictor agents are blunted during pregnancy. This has been mainly attributed to an increased production of endothelium-derived mediators. The objective of this work was to evaluate if pregnancy changes the relative participation of nitric oxide (NO) and prostaglandins (PG) in respect to the modulation of the increases in renal perfusion pressure induced by phenylephrine (Phe). Dose-response curves were made with gradually increasing doses of Phe using an isolated kidney preparation in the presence of a NO synthase (NOS) inhibitor (L-NAME, 1 microM), a PG-synthesis inhibitor (indomethacin, 1 microM), both, or neither. Also, renal cyclooxygenase (COX-1 and COX-2) and endothelial NOS (eNOS) expression was determined using PCR. The experiments were done in kidneys from nonpregnant and pregnant rats. Our results showed that the relative participation of renal vasoactive mediators seems to change during pregnancy. We found the presence of a COX-1-dependent vasoconstrictor in the middle of pregnancy that was not found in nonpregnant rats. Our results also suggest that there is increased participation of another renal vasodilator substance, the effect of which is observed when NO or PG synthesis is inhibited during late pregnancy. In addition, an apparent interaction between renal eNOS and COX-1 expression was observed: eNOS expression was diminished, while COX-1 was increased during the 2nd week of pregnancy. In contrast, in kidneys from the 3rd week of pregnancy, the expression of these two enzymes was similar.     

Extrathymic differentiation and antigen response of αβT lymphocytes in pregnancy

We studied reactivity of αβT-lymphocytes in CBA pregnant females toward male antigens and the presence of gene rearrangement in T-cells antigen receptor in peripheral lymphoid organs of mice in the case of three breeding variants: CBA × BALB/c (normal allogenic pregnancy), CBA × CBA (syngenetic pregnancy), and CBA × DBA/2 (prone to abortion combination). It was shown that proliferative response of αβT-lymphocytes in pregnant CBA females to male spleen cells was the most marked at normal allogenic pregnancy, the least marked at syngenic pregnancy, and was not observed at the combination CBA × DBA/2. In addition, cells of paraaortic lymphatic nodes (draining uterus) respond to male antigen reliably more effectively than lymphocytes in mesenterial and axillary lymphatic nodes. Simultaneous estimation of recombinase RAG-1, the key enzyme in rearrangement of T-receptor genes, revealed similar principles: predominant activity of recombinase in T-lymphocytes in paraaortal lymphatic nodes of CBA pregnant females. This points to the relationship between extrathymic rearrangement of antigen receptor genes and change in the antigen-detecting repertoire of these cells. The possible biological significance of the discovered phenomenon is discussed.     

Social behavior and genital swelling in pregnant chimpanzees (Pan troglodytes)

Previous reports of increased sexual activity associated with genital swelling during chimpanzee pregnancy have suggested that the tumescent pregnant female may be regarded as a regularly cycling estrous female. Analysis of additional data from seven pregnant and eight cycling females, however, indicated that tumescent pregnant females differed from cycling females in some social interactions with males. As in earlier reports, pregnant females were more receptive to male-initiated copulatory bouts. In addition, pregnant females initiated grooming bouts with males much less frequently than did cycling females, and males spent less time grooming and less frequently inspected the genitals of pregnant than cycling cagemates. This tendency to decrease social interaction during pregnancy is consistent with field reports that pregnant chimpanzees prefer the company of their offspring and other noncycling females. In addition, the genital swelling patterns of 40 chimpanzee pregnancies were analyzed. Length of gestation averaged 231.5 days. Although a high degree of individual variation existed, females were swollen an average of 41% of the days observed, yet reached maximum swelling only 8.7% of the time. Genital swelling was less frequent during the third trimester, averaging 50.5, 47.9, and 22.6% tumescent days in each trimester. Young pregnant females showed maximum swelling more often than did older females. This finding is discussed with respect to field reports of intercommunity transfer of young, tumescent female chimpanzees.     

Role of endogenous prostaglandins in pregnancy termination by 15-methyl PGF2α

Thirty pregnant women with foetal death in utero received 15-methyl PGF_2α to terminate their pregnancies. Two groups (15 cases each) matched for age, gravidity and age of pregnancy were studied. One group received indomethacin suppositories before and during the PG induction while the second group received the prostaglandin analogue therapy only. The group which received the prostaglandin biosynthesis inhibitor showed a longer induction-termination interval, more PG ampoules were used and the number of failed cases was higher. Thus, the Release of Endogenous prostaglandins seems to play a complementary role in the therapeutic termination of pregnancy.     

Attenuated glomerular arginine transport prevents hyperfiltration and induces HIF-1α in the pregnant uremic rat

Pregnancy worsens renal function in females with chronic renal failure (CRF) through an unknown mechanism. Reduced nitric oxide (NO) generation induces renal injury. Arginine transport by cationic amino acid transporter-1 (CAT-1), which governs endothelial NO generation, is reduced in both renal failure and pregnancy. We hypothesize that attenuated maternal glomerular arginine transport promotes renal damage in CRF pregnant rats. In uremic rats, pregnancy induced a significant decrease in glomerular arginine transport and cGMP generation (a measure of NO production) compared with CRF or pregnancy alone and these effects were prevented by l-arginine. While CAT-1 abundance was unchanged in all experimental groups, protein kinase C (PKC)-α, phosphorylated PKC-α (CAT-1 inhibitor), and phosphorylated CAT-1 were significantly augmented in CRF, pregnant, and pregnant CRF animals; phenomena that were prevented by coadministrating l-arginine. α-Tocopherol (PKC inhibitor) significantly increased arginine transport in both pregnant and CRF pregnant rats, effects that were attenuated by ex vivo incubation of glomeruli with PMA (a PKC stimulant). Renal histology revealed no differences between all experimental groups. Inulin and p-aminohippurate clearances failed to augment and renal cortical expression of hypoxia inducible factor-1α (HIF-1α) significantly increased in CRF pregnant rat, findings that were prevented by arginine. These studies suggest that in CRF rats, pregnancy induces a profound decrease in glomerular arginine transport, through posttranslational regulation of CAT-1 by PKC-α, resulting in attenuated NO generation. These events provoke renal damage manifested by upregulation of renal HIF-1α and loss of the ability to increase glomerular filtration rate during gestation.     

Acceleration of puberty in female mice by a chemosignal from pregnant and lactating females: circadian rhythm effects

Two experiments were designed to test whether the urinary chemosignal excreted by pregnant and lactating female mice that accelerates puberty in young females is affected by circadian rhythms. The experiments also measured the possible influence of circadian rhythms on the response of the young recipient females. For urine from both pregnant and lactating females there was no difference in the effectiveness for accelerating puberty in urine collected during all 24 h. However, pregnancy urine used for treatment at 1800 and 0000 h, and lactation urine used for treatment at 1800, 0000 and 0600 h, all resulted in significantly earlier mean ages for puberty than pregnancy urine treatment at 0600 or 1200 h, or lactation urine treatment at 1200 h. There was also a significant interaction between the time of urine collection and the time of urine treatment for each urine source; urine was generally more effective in accelerating sexual development when used for treating young females at the same hour at which it had been collected, or at the time interval(s) just before or after the time at which it had been collected.     

Coprophagy in female mice during pregnancy and lactation

Coprophagy in female mice was observed predominantly in the reproductive stage. Female mice exhibited coprophagy more frequently during pregnancy and ingested larger amounts of feces during pregnancy and lactation than when they were not pregnant. Feces were found to be rich in vitamin B12 and folic acid. However, there were no marked fluctuations in the levels of either vitamin in the feces during pregnancy or lactation as compared with levels when animals were not pregnant. Acceleration of coprophagy during pregnancy and lactation seemed to correlate with the increased nutritional requirements of females during the reproductive stage.     

Changes in endogenous urea recycling and the handling of renal urea in pregnant and lactating Sardi sheep kept on a constant feeding level

The kinetics of endogenous urea were compared during the last month of pregnancy, lactation, and a nonpregnant, nonlactating control period in Sardi sheep kept on a constant feed level. Urea entry rate estimated by injections of [14C]urea rose by 36% during pregnancy. Renal urea excretion was reduced by 40% during pregnancy and by 28% during lactation. Consequently, fractional urea recycling was greater during pregnancy and, to some extent, during lactation than during the control period. In a second series of experiments, glomerular filtration rate increased by 48% and urea filtration rate rose by 17% during pregnancy. During lactation, both glomerular filtration rate and urea filtration rate were close to control levels. It appears that the decreased renal urea excretion during pregnancy and lactation was due mainly to increased tubular reabsorption of urea. Rumination time increased by 15% during pregnancy. Rumen ammonia concentration was elevated in both pregnant and lactating ewes above the control period level. The results suggest that Sardi sheep possess a high potential for the conservation of nitrogen during pregnancy and lactation periods.     

Detection of pregnancy in a hibernator based on activity data

Pregnancy and parturition are often difficult to detect in wild-living animals, especially in species that give birth to altricial young in burrows or caves. Current methods to detect pregnancy and birth in hibernating animals often entail disturbances that can affect the animals' reproductive success. We developed a new method to confirm pregnancy and parturition in hibernating brown bears (Ursus arctos) using activity data recorded in dual-axis motion sensors mounted on GPS–GSM neck collars on 30 brown bears during 52 hibernation seasons in Sweden. We adjusted recorded activity to the individual basal activity level for each bear. Pregnant females showed characteristic activity patterns during the period of pregnancy, with significantly higher daily activity levels and frequency of active periods during pregnancy than nonpregnant bears. Pregnant females were active on average 2.20 times more often during the pregnancy period than during the postpartum period, compared with 0.97 times for nonpregnant females. A pregnancy index was defined as the average of the proportion of mean daily activity levels and the proportion of activity events during the pregnancy period compared with the postpartum period. It averaged 2.61?±?1.73 (SD) for pregnant females and 0.94?±?0.24 for nonpregnant females. Using this method, we evaluated a group of adult females that had an unverified reproductive status but were classified as not pregnant because no cubs had been observed after den emergence. The results suggested that 35 % of those females had, in fact, been pregnant.     

Urinary excretion of prostaglandin E2 and prostaglandin F2alpha in potassium-deficient rats

Potassium-deficiency was induced in rats by dietary deprivation of potassium. The animals became polyuric and urine osmolality decreased more then three-fold compared to controls. Urinary excretion of prostaglandin E2 (PGE2) and prostaglandin F2alpha (PGF2alpha) did not increase during 2 weeks of potassium depletion. Partial inhibition of renal prostaglandin synthesis by meclofenamate did not increase the urine osmolality after water deprivation. These results make unlikely the hypothesis that the polyuria of potassium-deficiency, is the result of enhanced renal synthesis of prostaglandins with subsequent antagonism of the hydro-osmotic effect of vasopressin. Male animals consistently excreted less PGE2 than female animals.     

Effects of anandamide on gestation in pregnant rats

The present study was to test whether the recently described endogenous ligand for the cannabinoid receptor; arachidonyl-ethanolamide (anandamide, ANA), may produce similar effects on pregnancy as the main psychoactive component of marihuana: Δ⁹-tetrahydrocannabinol (THC) in rats. ANA, THC (0.02 mg/kg i.p./day, respectively) or vehicle were injected daily over the third week of pregnancy. The pregnant rats were either killed on day 21 of pregnancy or followed up to delivery. Results show a significant increase in the duration of pregnancy after both THC and ANA treatment. Both drugs caused an increase in the frequency of stillbirths. The mothers' hormone contents in tissues and sera were measured. Decreased LH content was observed in the serum of treated animals. No changes in FSH content were observed either in the pituitary or in the sera. Pituitary prolactin (PRL) levels was lower in ANA treated animals as compared both to controls or THC treated subjects. The serum PRL content decreased in all experimental groups. Decrease in serum progesterone was more prominent in treated rats. Serum levels of prostaglandins (PGF 1 and PGF 2) were significantly decreased after THC and ANA treatment. We conclude that ANA has the same tendency to change reproductory parameters in pregnant rats as THC, although in some cases the effects of ANA were slightly different from that of THC. Both endogenous and exogenous cannabinoids inhibit PG synthesis in pregnant rats and this maybe responsible for the delay constitute the mechanism in the onset of labour.     

Attenuation of corticotropin-releasing hormone and arginine vasopressin responsiveness during late-gestation pregnancy in sheep

Responsiveness of the hypothalamo-pituitary-adrenal axis is decreased during pregnancy. Therefore, the objective of the present study was to determine if responsiveness at the level of individual corticotrophs to corticotropin-releasing hormone (CRH) or arginine vasopressin (AVP) is decreased during pregnancy in sheep. Anterior pituitaries (APs) were collected from pregnant and nonpregnant ewes. Half of the APs were dispersed, and cells were placed on immobilon and treated with vehicle, CRH (10 nM), or AVP (100 nM) for 2 h. Cells were then fixed and incubated with ACTH or pro-opiomelanocortin (POMC) antibodies. The percentage of cells staining positive for immunoreactive (ir) ACTH or POMC, the percentage of cells secreting irACTH or POMC, and the area of irACTH or POMC secretion were measured. RNA was extracted from the other half of the APs to quantify CRH type 1 (CRH-R1) and vasopressin type 1b (V1b) receptor mRNA by ribonuclease protection assay. CRH treatment increased the percentage of corticotrophs with relatively large areas of irACTH and POMC secretion in nonpregnant, but not in pregnant, ewes. AVP treatment significantly increased the percentage of irACTH- and POMC-secreting cells in nonpregnant, but not in pregnant, ewes. V1b receptor mRNA, but not CRH-R1 receptor mRNA, was significantly decreased during pregnancy. These results suggest that corticotroph responsiveness to CRH and AVP is decreased during pregnancy in sheep. Therefore, reduced corticotroph responsiveness may contribute to stress hyporesponsivity during pregnancy.     

Sex differences in vasopressin V₂ receptor expression and vasopressin-induced antidiuresis

The renal vasopressin V(2) receptor (V(2)R) plays a critical role in physiological and pathophysiological processes associated with arginine vasopressin (AVP)-induced antidiuresis. Because clinical data suggests that females may be more prone to hyponatremia from AVP-mediated antidiuresis, we investigated whether there are sex differences in the expression and function of the renal V(2)R. In normal Sprague-Dawley rat kidneys, V(2)R mRNA and protein expression was 2.6- and 1.7-fold higher, respectively, in females compared with males. To investigate the potential physiological implications of this sex difference, we studied changes in urine osmolality induced by the AVP V(2)R agonist desmopressin. In response to different doses of desmopressin, there was a graded increase in urine osmolality and decrease in urine volume during a 24-h infusion. Females showed greater mean increases in urine osmolality and greater mean decreases in urine volume at 0.5 and 5.0 ng/h infusion rates. We also studied renal escape from antidiuresis produced by water loading in rats infused with desmopressin (5.0 ng/h). After 5 days of water loading, urine osmolality of both female and male rats escaped to the same degree physiologically, but V(2)R mRNA and protein in female kidneys was reduced to a greater degree (-63% and -73%, respectively) than in males (-32% and -48%, respectively). By the end of the 5-day escape period, renal V(2)R mRNA and protein expression were reduced to the same relative levels in males and females, thereby abolishing the sex differences in V(2)R expression seen in the basal state. Our results demonstrate that female rats express significantly more V(2)R mRNA and protein in kidneys than males, and that this results physiologically in a greater sensitivity to V(2)R agonist administration. The potential pathophysiological implications of these results are that females may be more susceptible to the development of dilutional hyponatremia because of a greater sensitivity to endogenously secreted AVP.