Intact Fetuses Research Articles

Afferent and efferent components of the cardiovascular reflex responses to acute hypoxia in term fetal sheep.

1. We studied the effects of acute isocapnic hypoxia on arterial and central venous pressures, carotid and femoral blood flows and heart rate in intact and carotid denervated fetal sheep between 118 and 125 days gestation, after pre-treatment with either saline, atropine or phentolamine. Electrocortical activity (ECoG) and the incidence of fetal breathing movements (FBM) were also compared between intact and carotid denervated fetuses. 2. There were no significant differences between intact and denervated fetuses in any variable measured during normoxia. Soon after the onset of hypoxia a marked bradycardia occurred in intact, but not in denervated fetuses. Femoral blood flow and femoral vascular resistance (perfusion pressure/femoral blood flow) increased in intact, but not in denervated fetuses. Carotid blood flow increased in both groups of fetuses during hypoxia, but carotid vascular resistance did not change. During hypoxia, the incidence of FBM and low-voltage ECoG was similarly reduced in both groups of fetuses. 3. Atropine produced a rise in fetal heart rate during the control period in intact but not in denervated fetuses. At the onset of hypoxia atropine prevented the initial bradycardia seen in intact fetuses. In denervated fetuses a further increase in heart rate occurred throughout the hypoxia. 4. All denervated fetuses treated with phentolamine died during the hypoxic challenge, but nine out of fourteen intact fetuses treated with phentolamine survived. 5. In intact fetuses which survived hypoxia after treatment with phentolamine, the increase in arterial blood pressure was smaller and the increase in femoral resistance did not occur. In these fetuses a rise in heart rate occurred in hypoxia. Carotid vascular resistance decreased during hypoxia after administration of phentolamine. 6. Our results indicate that the initial cardiovascular responses of the late gestation sheep fetus to hypoxia are reflex, and that the carotid chemoreceptors provide the afferent limb of this reflex. The bradycardia is mediated through a muscarinic pathway, as it is blocked by atropine. The femoral vasoconstriction is mediated through an alpha-adrenergic mechanism, mediated both neurally by a carotid chemoreflex and via catecholamines released directly from the adrenal medulla. Both these components are blocked by phentolamine. 7. The differences in survival between intact and denervated fetuses during hypoxia after phentolamine suggest that the carotid chemoreflex response to hypoxia involves mechanisms in addition to vagal efferents to the heart and alpha-adrenergic actions at peripheral blood vessels.(ABSTRACT TRUNCATED AT 400 WORDS)

The adrenocorticotropic hormone and arginine vasopressin responses to hypercapnia in fetal and maternal sheep.

Previous studies have demonstrated that fetal adrenocorticotropic hormone (ACTH) and arginine vasopressin (AVP) are increased during periods of acidemia produced by infusion of acid intravenously or by acidemia secondary to hypovolemia. The purpose of this study was to quantify ACTH and AVP responses to hypercapnic acidemia and to test the role of the peripheral chemoreceptors in the control of these responses. Chronically catheterized fetal sheep were subjected to carotid sinus denervation and bilateral vagotomy or were studied intact. At least 5 days after surgery, fetuses were exposed to a 60-min period of normocapnia or hypercapnia, delivered via a polyethylene bag containing 5-8% CO2 in 21% O2 fitted over the head of the pregnant ewe. Hypercapnia significantly increased fetal arterial PCO2 to 55.2 +/- 1.8 and 55.9 +/- 2.2 mmHg and decreased arterial pH to 7.257 +/- 0.011 and 7.281 +/- 0.010 in intact and denervated fetuses, respectively. Fetal mean arterial blood pressure was decreased slightly in the denervated fetuses during hypercapnia. Fetal plasma AVP was increased in both groups equally, and plasma ACTH and cortisol were increased in the denervated fetuses only. Fetal heart rate was increased significantly in intact but not denervated fetuses. We conclude that respiratory acidemia is a mild stimulus to AVP secretion and that this response is not attenuated by peripheral chemodenervation.

Endocrine regulation of fetal adipose tissue metabolism in the pig: role of thyroxine.

This study was performed to characterize the role of thyroxine (T4) in the regulation of fetal adipose tissue metabolism. On day 70 of gestation, pig fetuses were hypophysectomized (hypoxed) by microcauterization. Both hypoxed and intact fetuses were implanted subcutaneously with T4 pellets or received no hormone replacement. Fetuses were removed by laparotomy on day 90 of gestation. Additional fetuses were hypoxed on day 70, implanted with T4 pellets on day 90 and removed on day 105 of gestation. Serum T4 levels were similar in hypox + T4 and intact + T4 fetuses and increased in both groups relative to their respective controls. T4 supplementation restored the lipolytic response to isoproterenol and enhanced the response to dibutyryl cyclic AMP at 90 days in hypoxed animals but had no effect on basal or stimulated lipolysis in intact fetuses. T4 induced a dramatic increase in lipogenesis in hypoxed fetuses when administered during either fetal period and produced a slight though significant increase in basal lipogenesis in intact fetuses when administered from days 70 to 90 of gestation. However, T4 had no effect on basal or insulin-stimulated lipogenesis in intact fetuses when administered from days 90 to 105 of gestation. These results indicate that T4 may have a primary influence on fetal adipose tissue metabolism only in the absence of inhibition from counterregulatory hormones of pituitary origin.

Distribution of Expression of Cell Adhesion Molecules in the Mid to Late Gestational Mouse Fetus

The control of murine morphogenesis appears to be regulated in part by the expression of the primary cell adhesion molecules, such as the neural cell adhesion molecules (N-CAM). Here we show that the epithelial cell adhesion molecules appear in intestinal epithelium, liver and cartilage, but were absent from intestinal submucosa and neural tissues. N-CAMs on the other hand were present in intestinal submucosa and neural tissues, but absent from intestinal epithelium, liver, and cartilage. Both epithelial cell adhesion molecules and N-CAM were present in intestinal primordium at gestation times (days 12 and 13) when intestinal epithelium and submucosa are not morphologically distinguishable. On day 14 of gestation, when the intestinal epithelium and submucosa are morphologically distinguishable, epithelial cell adhesion molecules are present in intestinal epithelium but not submucosa while N-CAM has the reciprocal pattern of expression. Immunoblots with antibodies to N-CAM revealed two bands of 110-220 and 60 kD which followed specific patterns of expression. As defined by densitometry, the intensity of the larger protein increased from day 12 to 18 in neural tissue groups, but diminished in late gestational intestine and intact fetus and was replaced by a more discrete region of 110-150 kD, suggesting that embryonic to adult conversion of isoform ('E to A conversion') had occurred at this nonneural site.

The influence of thyroxine on the differentiation of adipose tissue and skin during fetal development.

Preobese fetuses have elevated thyroid hormone levels and depressed growth hormone levels relative to lean fetuses. Therefore, we are studying various experimental fetal pig models to explore the relationship between endocrine status and onset of obesity. In the present study, intact and hypophysectomized (d 70) fetuses were implanted with thyroxine (T4) pellets on d 70 of gestation, and blood, adipose tissue, and skin samples were obtained upon removal of d 90 of gestation. Body weights were similar for all groups and T4 treatment reversed myxedema in hypophysectomized fetuses. Serum T4 levels were elevated (p less than 0.05) and skin and hair development were enhanced (p less than 0.05) to a similar degree by T4 treatment in intact and hypophysectomized fetuses. However, T4 did not influence adipose tissue development in intact fetuses, but markedly enhanced development in hypophysectomized fetuses. For instance, fat cell size and lipogenic enzyme activities in hypophysectomized fetuses were increased (p less than 0.05) by 5-mg and 15-mg T4 treatments, with a marked increase (p less than 0.05) in apparent fat cell number with the 15-mg T4 treatment. In contrast, there was no effect of T4 (15 mg) on these parameters in intact fetuses. Therefore, fetal obesity may be directly associated with elevated thyroid hormone levels and suppressed growth hormone levels, but not with elevated T4 levels alone.

Reflex control of fetal arterial pressure and hormonal responses to slow hemorrhage

Late-gestation fetal sheep respond to slow hemorrhage with increases in plasma concentrations of adrenocorticotropic hormone (ACTH), hydrocortisone, arginine vasopressin (AVP), and plasma renin activity (PRA) that correlate to the acidemia and hypercapnia also produced by hemorrhage. This study was designed to investigate the role of peripheral chemoreceptors in the mediation of these responses. Chronically catheterized fetal sheep were left intact or were subjected to bilateral section of cervical vagosympathetic trunks and carotid sinus nerves. At least 5 days after surgical preparation (between 121 and 138 days of gestation) fetuses were bled at a rate of 11 ml/10 min for 2 h. Denervated fetuses were studied with or without simultaneous infusion of phenylephrine. Denervation exaggerated the decrease in mean arterial pressure and arterial pH and the increase in arterial PCO2 during hemorrhage. Infusion of phenylephrine in the denervated fetuses prevented the decrease in blood pressure and reduced the magnitudes of changes in blood gases. Fetal plasma ACTH, hydrocortisone, and PRA responses to the hemorrhage were exaggerated in the denervated fetuses (not infused with phenylephrine) compared with the intact fetuses. Phenylephrine infusion attenuated the ACTH response and inhibited the AVP response but did not alter the PRA response. We conclude that the sectioned fibers are important for the maintenance of blood pressure and blood gases during hemorrhage and that the PRA, AVP, and ACTH responses to slow hemorrhage are not mediated by peripheral chemoreceptors.

Cardiovascular Responses to Hypoxemia in Sinoaortic-Denervated Fetal Sheep

Fetal cardiovascular response to acute hypoxemia is characterized by bradycardia, hypertension, and redistribution of cardiac output. The role of aortic and carotid chemoreceptors in mediating these responses was examined in eight sinoaortic-denervated and nine shamoperated fetal lambs. Blood gases, pH, heart rate, arterial pressure, and blood flow distribution were determined before and during hypoxemia. In intact fetuses, heart rate fell from 184 +/- 12 to 165 +/- 23 beats/min (p less than 0.01) but increased from 184 +/- 22 to 200 +/- 16 beats/min (p less than 0.05) in the sinoaortic-denervated fetuses. Intact fetuses showed an early hypertensive response to hypoxemia, whereas the sinoaortic-denervated fetuses developed a delayed, progressive rise in blood pressure. In both groups, fetal cardiac output and umbilical blood flow were maintained; cerebral, myocardial, and adrenal blood flow increased, and pulmonary blood flow decreased. Peripheral blood flow decreased 39% (p less than 0.001) in intact fetuses but was maintained in sinoaortic-denervated fetuses. Vascular responses to hypoxia in the brain, heart, adrenal, and lungs are regulated primarily by direct local effects. During hypoxemia, peripheral chemoreceptors mediate bradycardia and peripheral vasoconstriction but do not appear to be crucial for immediate fetal survival.

Umbilical cord occlusion stimulates breathing independent of blood gases and pH

The role of umbilical cord occlusion in the initiation of breathing at birth was investigated by use of 16 unanesthetized fetal sheep near full term. Artificial ventilation with high-frequency oscillation was used to control fetal arterial blood gas tensions. At baseline, PCO2 was maintained at control fetal values and PO2 was elevated to between 25 and 50 Torr. In the first study on six intact and four vagotomized fetuses, arterial PCO2 and PO2 were maintained constant during two 30-min periods of umbilical cord occlusion. Nevertheless, the mean fetal breathing rate increased significantly when the umbilical cord was occluded. In the second study on six intact fetuses, hypercapnia (68 Torr) was imposed by adding CO2 to the ventilation gas. When the umbilical cord was occluded, there was a significantly greater stimulation of breathing (rate, incidence, and amplitude) in response to hypercapnia than in response to hypercapnia alone. During cord occlusion, plasma prostaglandin E2 concentration decreased significantly. Results indicate that cord occlusion stimulates breathing possibly by causing the removal of a placentally produced respiratory inhibitor such as prostaglandin E2 from the circulation.

Onset of the Constrictive Effect of Indomethacin on the Ductus arteriosus in Fetal Rats

The time of onset of the constrictive effect of indomethacin on the ductus arteriosus (DA) in fetal rats was assessed by measurement of the caliber of the DA after maternal treatment with indomethacin on days 19-21 of gestation. The day following overnight mating was regarded as day 0 of gestation. Observation was performed by direct exposure of the DA by hand shaving of intact frozen fetuses. On days 20 and 21, the DA was significantly constricted 3 h after maternal treatment with 1 mg/kg of indomethacin. When the DA was examined at 19 1/2 and 19 2/3 days of gestation (3 h after indomethacin exposure), it was significantly constricted at 19 2/3 days but not at 19 1/2 days. Higher doses of indomethacin (10 and 100 mg/kg) induced a significant constriction of the DA at day 19 1/2, but not at the beginning of the same day (1.00 a.m.). These results suggest that the onset of the susceptibility of the DA to the constrictive effect of indomethacin occurs in the first half of day 19 of gestation.

Role of renal sympathetic nerves in response of the ovine fetus to volume expansion

To investigate the role of renal sympathetic nerves in the fetal response to hypervolemia, studies were carried out in conscious, chronically instrumented fetal sheep aged 137-142 days of gestation. Bilateral renal denervation (n = 9) or sham surgery (n = 8) was carried out under halothane anesthesia 3-6 days before experiments. Bilateral renal denervation did not alter basal fetal renal hemodynamics, glomerular filtration rate (GFR), or Na+ excretion. Volume expansion with 6% Dextran 70 (18 ml/kg) was associated with a fall in fetal hematocrit, a sustained increase in mean arterial blood pressure, and a sustained diuresis and natriuresis. There was no significant change in GFR during fetal hypervolemia from control levels of 4.51 +/- 0.74 ml/min (intact) and 4.43 +/- 0.43 ml/min (denervated). Atrial natriuretic factor increased from 144 +/- 34 to 464 +/- 134 pg/ml, and plasma renin activity decreased from 5.15 +/- 1.7 to 3.04 +/- 1.0 ng.ml-1.h-1 in intact animals, within 30 min of completion of the dextran infusion. Similar changes occurred in denervated fetuses. Plasma aldosterone levels remained constant in intact and denervated fetuses during hypervolemia at control levels of 40.8 +/- 5.4 and 59.3 +/- 8.4 pg/ml, respectively. These findings suggest that renal sympathetic nerves do not influence basal renal hemodynamics or function and do not appear to play an important role in the natriuretic response to volume expansion during fetal life. This can be explained by a low tonic renal nerve activity before birth.

Effect of Cortisol Infusion on Basal and Corticotropin-eleasing Factor (CRF)-Stimulated Plasma ACTH Concentrations in the Sheep Fetus after Surgical Isolation of the Pituitary*

Although it has been demonstrated that glucocorticoids can inhibit basal and stimulus-induced increase in fetal plasma ACTH concentrations, the site(s) of action of the glucocorticoids in the fetal hypothalamo-pituitary axis are unclear. We have investigated the ontogeny of the negative feedback effect of cortisol on basal and CRF-stimulated ACTH secretion in intact fetal sheep and in fetal sheep after surgical disconnection of the hypothalamus and pituitary (HPD). In saline-pretreated fetal sheep there was a significant increase in plasma ACTH concentrations in response to an ovine CRF (oCRF) bolus (1 microgram) in HPD and intact fetuses at 120-128 days and at 138-149 days gestation. In the intact group the ACTH response at 120-240 min after oCRF was significantly lower (P less than 0.01) after 138 days compared with before 128 days. In this group the cortisol response during the first hour after oCRF was significantly greater (P less than 0.005) after 138 days than in the younger fetuses. In the HPD group there was no significant difference between the two gestational age ranges in either the ACTH or cortisol responses to oCRF. Between 120 and 128 days gestation, increasing plasma cortisol concentrations (110-170 nmol/liter above baseline values) by exogenous infusion had no significant effect on the basal fetal plasma ACTH concentrations in HPD or in intact fetuses. In contrast, after 138 days gestation, the basal plasma ACTH concentrations were significantly decreased by 50% during the cortisol infusion period in the intact but not in the HPD group. It would appear therefore, that the development of the negative feedback action of cortisol to suppress basal fetal plasma concentrations of ACTH is dependent on the presence of a functional fetal hypothalamus. In HPD and intact fetuses cortisol infusion abolished the fetal ACTH response to the oCRF bolus from as early as 120 days gestation. Thus the negative feedback action of cortisol on the CRF-induced increases in fetal plasma ACTH concentrations can occur directly at the fetal pituitary.

Peripheral chemoreceptor control of fetal renin responses to hypoxia and hypercapnia.

The renin response to hypoxia in late gestation fetal sheep has been well characterized. However, the renin response to asphyxia--the combination of hypoxia and hypercapnia--has not been extensively studied. The purpose of this study was to determine 1) the interaction of hypoxia and hypercapnia in the control of renin secretion in late gestation fetal sheep and 2) the role of peripheral arterial chemoreceptors therein. Chronically catheterized fetal sheep (intact or sinoaortic denervated) were exposed to hypoxia and/or hypercapnia for 30 minutes. Hypercapnia alone had no effect on plasma renin activity or aldosterone but did result in a significant increase in angiotensin II. Hypercapnia combined with hypoxia resulted in a significant increase in renin activity, angiotensin II, and aldosterone. Sinoaortic denervation attenuated the renin and angiotensin II responses to hypercapnia plus hypoxia. The increase in renin and angiotensin II in response to hypercapnia with or without concomitant hypoxia strongly correlated with the magnitude of the decrease in arterial pH in intact fetuses only. Hypoxia alone and in concert with hypercapnia increased mean arterial pressure and decreased heart rate in intact but not sinoaortic denervated fetuses. We conclude that 1) hypercapnia more potently increases plasma renin activity than does hypoxia in late gestation fetal sheep, 2) arterial pH may be the relevant signal perceived by the peripheral arterial chemoreceptors for the control of the renin-angiotensin system during asphyxia, and 3) the cardiovascular response to hypoxia is mediated, in part, by peripheral arterial chemoreceptors.

Stimulation of ovine placental transport of calcium and magnesium by mid‐molecule fragments of human parathyroid hormone‐related protein

Perfusion in situ of the placenta of intact or previously parathyroidectomized fetal lambs has been used to assess the ability of three mid-molecule fragments of the human parathyroid hormone-related protein (PTHrP) molecule to stimulate the placental transport of calcium and magnesium. PTHrP(67-86 amide) was most effective but some activity was also shown by PTHrP(75-86 amide) and by PTHrP (75-84) in decreasing order. This placental action of PTHrP(67-86 amide) was rapid and could be observed using the placenta from an intact fetus, whereas it was necessary to use the placenta from a previously parathyroidectomized fetus to demonstrate stimulation of placental calcium transport by PTHrP(1-84). PTHrP(67-86 amide) may resemble the molecule that activates the placental calcium pump.

Fetal adrenal medulla catecholamine response to hypoxia-direct and neural components

In the fetus, the adrenal medullary catecholamine responses to hypoxia are mediated by direct and neural mechanisms. The present study determined the maturation of these responses in unanesthetized ovine fetuses from 109 to 136 days gestation. In intact fetuses at 109-119 days gestation, hypoxia lowered arterial PO2 from 23.4 +/- 0.9 to 9.5 +/- 0.4 mmHg and induced acute increases in plasma norepinephrine (P less than 10(-5)) and epinephrine (P less than 10(-5)) concentrations. Fetuses at 130-136 days gestation showed similar changes in PO2 and plasma catecholamines as in younger fetuses. Blockade of neural input to the adrenal by hexamethonium (25 mg/kg) reduced but did not eliminate the increases in plasma norepinephrine and epinephrine concentrations in fetuses at 109-119 days gestation, while it completely abolished these responses in fetuses at 130-136 days gestation. These results suggest that in unanesthetized ovine fetuses a direct response of the adrenal medulla to hypoxia is present at 110 days gestation. In contrast, at 130 days gestation the response to hypoxia is entirely neurally mediated. Thus neural innervation to the ovine fetal adrenal medulla matures before 110 days gestation, much earlier than previously reported.

Endocrine Regulation of Tissue Glucose-6-Phosphatase Activity in the Fetal Sheep during Late Gestation*

Endocrine regulation of tissue glucose-6-phosphatase activity in utero was examined by measuring enzyme levels in liver and kidneys of fetal sheep during the second half of gestation and after experimental manipulation of fetal plasma cortisol and insulin levels. Tissue glucose-6-phosphatase activities increased toward term in parallel with the rise in fetal plasma cortisol. At birth, the activities were significantly higher than in utero, but significantly less than in adult nonpregnant sheep. Fetal hypophysectomy lowered fetal plasma cortisol and reduced hepatic and renal glucose-6-phosphatase activities compared with those in intact fetuses near term. Conversely, intrafetal cortisol infusion raised fetal plasma cortisol and significantly increased tissue glucose-6-phosphatase activity to values similar to those in older fetuses. When the data from these groups of fetuses and the newborn lambs were combined, there was a significant positive correlation between the plasma cortisol level and the glucose-6-phosphatase activity in both liver and kidney. Fetal hypoinsulinemia was induced by fasting the ewe for 48 h and by fetal pancreatectomy. Fetal hepatic and renal glucose-6-phosphatase activities were higher in fasted than in fed animals, while pancreatectomy had little apparent effect on enzyme activity in either tissue. However, when differences in plasma cortisol were taken into account, hepatic, but not renal, glucose-6-phosphatase activities were higher in both groups of hypoinsulinemic fetuses than would have been observed in normoinsulinemic animals with a similar plasma cortisol level. Partial correlation analysis of the data showed that plasma insulin and cortisol were both significant influences on hepatic glucose-6-phosphatase activity in utero, but plasma cortisol had the more pronounced effect. Cortisol, therefore, appears to be a physiological regulator of tissue glucose-6-phosphatase activity in utero and enhances the glucogenic capacity of the sheep fetus during late gestation.

Control of organ blood flow in fetal sheep during normoxia and hypoxia.

The role of peripheral chemoreceptors in the circulatory adaptation to hypoxia and the effects of rapid-eye-movement (REM) and non-REM (NREM) sleep and breathing activity on organ blood flow were assessed in fetal sheep. Blood flow was measured with isotope-labeled microspheres on intact, vagotomized (VX), and sinoaortic-denervated (SAD) fetuses. Denervation did not change the biventricular cardiac output (Biv. CO) or organ blood flows during normoxia. In intact fetuses the blood flow was increased during hypoxemia in brain, adrenals, and heart but not in kidneys, skeletal muscles, or placenta. The increase in organ blood flow during hypoxemia was reduced in the VX group and even more in SAD fetuses, but in the latter group, blood flow was still increased in mid-brain, medulla, pons, skeletal muscles, and heart. Sleep states per se did not significantly affect the blood flow to any organs tested. However, the Biv. CO and blood flow to all organs except kidneys and adrenals was increased during fetal breathing in REM sleep. We conclude that 1) during moderate hypoxemia both aortic and carotid bodies plus an additional mechanism are involved in redistributing fetal blood flow, and 2) changes in organ perfusion during REM sleep are due to concomitant fetal breathing.

Modulation of fetal cardiovascular responsiveness to norepinephrine by autonomic nervous system.

To determine the extent to which the autonomic nervous system modifies the fetal cardiovascular responses to exogenous norepinephrine (NE), NE was infused intravenously (0.39-39 micrograms/min) for 30 min into chronically catheterized sheep fetuses averaging 132 days gestation. The resulting changes in arterial pressure, venous pressure, heart rate, and blood volume were compared between fetuses with and without ganglionic blockade. Autonomic blockade did not alter the relationship between the rise in NE concentration and NE infusion rate. In fetuses with a blocked autonomic nervous system, the arterial pressure response to exogenous NE was shifted 0.8 log units to the left when compared with normal fetuses. The venous pressure response to NE infusion was not altered in the blocked fetuses when compared with normal fetuses. Heart rate in the autonomically blocked fetuses increased with plasma NE concentration, which was opposite to the initial suppression of heart rate during NE infusion in control fetuses. Fetal blood volume decreased progressively with increasing NE infusion rate in the blocked fetuses, which was similar in autonomically intact fetuses, except for an increase in blood volume at low NE infusion rates. Thus it appears that the autonomic nervous system modifies the fetal arterial pressure, heart rate, and blood volume responses to exogenous NE but not the response of venous pressure.

Fetal control of calcium transport across the rat placenta.

Control of maternofetal calcium transfer across the in situ perfused rat placenta at day 21 of gestation (term 23 d) was investigated in both intact fetuses and those parathyroidectomized by decapitation on day 19. Decapitation resulted in significant fetal hypocalcemia. Injection of fetuses subcutaneously through the uterine wall with 0.43 micrograms bovine (b) PTH(1-84), 20 ng 1,25(OH)2D3 or 10 microL of the appropriate diluent resulted 2 h later in a raised fetal blood ionized Ca concentration only with bPTH(1-84) in both normal and decapitated fetuses. Fetal decapitation caused a significant (p less than 0.001) fall in the clearance of 45Ca across the placenta (Kmf45Ca), which was significantly (p less than 0.05) reversed after fetal bPTH(1-84) and 1,25 dihydroxy vitamin D3 (1,25(OH)2D3) injection, but not back to normal levels. There was no effect of either hormone on Kmf45Ca in placentas from intact fetuses, or on Kmf51Cr-EDTA (used as an extracellular marker) in either group. When 4 ng/mL r[Nle8,21, Tyr34] PTH(1-34), 50 pg/mL 1,25(OH)2D3 or the appropriate diluent was perfused through placentas the only response observed was a significant (p less than 0.05) increase in Kmf45Ca with 1,25(OH)2D3 perfusion in placentas from decapitated fetuses, Kmf51Cr-EDTA being unchanged. Finally, perfusion with 10(-5) M forskolin (an activator of adenylate cyclase) stimulated Kmf45Ca in placentas from both normal and decapitated fetuses. Although there was also some effect on Kmf51Cr-EDTA in the latter, there was none in the placentas from normal fetuses, and here the effect on Kmf45Ca was dose dependent with an initial response at 10(-6) M.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular effects of dynorphin A-(1-13) and arginine vasopressin in fetal lambs

The cardiovascular effects of the kappa-opioid receptor agonist, dynorphin A-(1-13) (D13), were compared with those of arginine vasopressin (AVP) in intact and bilaterally vagotomized (VGX) fetal lambs. Intravenous injection of AVP (114 ng/kg) produced a significant rise in mean arterial pressure (MAP) lasting 15-20 min in both intact and VGX lambs. AVP produced a bradycardia in intact fetuses concurrently with the MAP response and had no effect on heart rate (HR) in VGX fetuses. D13 (500 micrograms/kg) also produced significant increases in MAP in intact and VGX fetuses that lasted 45-60 min. D13 produced a bradycardia in intact fetal lambs but, unlike AVP, significantly increased HR in VGX fetuses. HR responses to D13 had time courses similar to MAP responses in both intact and VGX fetal lambs. Pretreatment with a vasopressin V1-receptor antagonist significantly attenuated pressor responses to AVP in both treatment groups and to D13 in intact fetuses and abolished the D13 pressor response in VGX fetuses. The antagonist also completely blocked HR responses to AVP in intact and to D13 in VGX fetuses and attenuated the D13 HR response in intact fetuses. Therefore the effects of D13 on ovine fetal cardiovascular function appear to be mediated in part through AVP pathways. D13 also appears to have a positive chronotropic effect on the heart that is normally masked by inhibitory vagal activity.

On the distribution and morpho-functional characteristics of 5-HT-immunoreactive cells in the hypothalamus of fetuses and neonatal rats

This study attempted to visualize serotonin (5-HT)-immunoreactive (IR) neurons in the hypothalamus of intact fetuses (E18) and neonatal rats (P9) as well as after their pretreatment with some drugs interfering with the 5-HT metabolism and uptake in the serotoninergic neurons ( l-tryptophan, pargyline, 5-hydroxytryptophan, fluoxetine). The 5-HT-IR cells were not observed in the hypothalamus of normal, untreated fetuses and neonatal rats. However, two large accumulations of 5-HT-IR neurons appeared in the anterolateral hypothalamus and in the dorsomedial nucleus after the subsequent injections of the monoamine oxidase inhibitor, pargyline, and the amino acid precursor of the 5-HT synthesis, l-tryptophan. A significantly less intensive reaction was observed after injections either of the second precursor of the 5-HT synthesis, 5-hydroxytryptophan instead of l-tryptophan, or pargyline only. Immunostaining, provoked by the pargyline and l-tryptophan pretreatment, was completely blocked by the injection of the specific 5-HT uptake inhibitor, fluoxetine. It means that the 5-HT immunostaining of the hypothalamic neurons may be accounted for by their capacity to take up specifically 5-HT from the environment rather than by its intraneuronal synthesis from l-tryptophan. Nevertheless, the 5-HT synthesis from 5-hydroxytryptophan in these cells cannot be excluded. The uptake of extracellular 5-HT into catecholaminergic neurons can be excluded as nomifensine, the specific inhibitor of the uptake to these neurons, did not modify the immunostaining.