Search PubMed⌕ Search

Biomedical subjects

J C Porter

Publications and source records attributed to J C Porter.

At least 73 records · Page 4Linked to original sources
PubMed1986

Hormonal modulation of the quantity and in situ activity of tyrosine hydroxylase in neurites of the median eminence.

The role of ovarian hormones in the control of the quantity and activity of tyrosine hydroxylase (TyrOHase) in neurites of the median eminence of the rat was investigated. TyrOHase was quantified by an immunoblot assay using purified rat TyrOHase as the standard. Treatment of ovariectomized animals with progesterone, but not estradiol, resulted in a significant reduction in the amount of TyrOHase in the median eminence. The in situ activity of the enzyme was assayed by measuring the rate of synthesis of L-3,4-dihydroxyphenylalanine (dopa), and the results were expressed as mol of dopa per hr per mol of TyrOHase. In animals treated with both estradiol and progesterone for 3 days, the in situ activity of TyrOHase in the median eminence was 114 +/- 13.5 (mean +/- SEM) compared to 26 +/- 4.7 for the controls. Estradiol or progesterone alone was much less effective than was the combination of estradiol and progesterone. To ascertain whether the effect of estradiol and progesterone on TyrOHase activity was reflected in the secretion of dopamine into hypophyseal portal blood, ovariectomized rats were treated for 3 days with both estradiol and progesterone or with the solvent vehicle. The concentration of dopamine in portal plasma of the hormone-treated animals was 1.93 +/- 0.533 ng/ml compared to 0.34 +/- 0.094 ng/ml in vehicle-treated animals. We conclude that the quantity and in situ molar activity of TyrOHase in neurites of the median eminence as well as the secretion of dopamine from these neurites are modulated by the combined action of estradiol and progesterone.

Animals↗
PubMed1986

Urinary arginine vasopressin: pattern of excretion in the neonatal period.

The pattern of arginine vasopressin (AVP) secretion in the immediate neonatal period is unclear. Plasma concentrations of AVP are reflected by its urinary excretion, thus providing a noninvasive method for studying the pattern of AVP release in the neonate. In these studies, we determined the pattern of urinary AVP excretion (microU/mg creatinine) during the first 2-4 days after birth in 78 neonates, 53 of whom had various prenatal and/or neonatal complications. In well term (n = 12) and preterm (n = 13) infants mean urinary AVP excretion decreased gradually during the first 24-36 h after birth. Although term and preterm infants with perinatal asphyxia had highest initial levels of urinary AVP (greater than 200 microU/mg creatinine) and a significant negative correlation with the 1-min Apgar score was obtained, their pattern of excretion was similar to respective controls. After delivery, elevated values for urinary AVP excretion were found among infants with neonatal courses complicated by intracranial hemorrhage, hypoxic encephalopathy, and pneumothorax. Urine osmolality did not correlate linearly with urinary AVP levels, but rather attained a maximum value of approximately 400 mosmol/kg at urinary AVP levels less than 200 microU/mg creatinine and then plateaued. It is concluded that the decrease in urinary AVP excretion observed soon after birth generally reflects diminution of the hypersecretion of AVP during parturition; neonates with evidence of intrapartum asphyxia initially have increased urinary AVP excretion; however, the pattern of excretion is similar to normal infants. During the neonatal period insults such as pneumothorax and intracranial hemorrhage may cause hypersecretion of this hormone.

Amniotic Fluid↗
PubMed1986

Prolactin levels in umbilical cord serum and its relation to fetal adrenal activity in newborns of women with pregnancy-induced hypertension.

The effect of hypertension in pregnant women on fetal maturation is an issue of considerable importance. Because of a possible role of prolactin in fetal adrenal steroidogenesis and in fetal lung maturation, we have investigated the relationship between hypertension in pregnant women and levels of prolactin and dehydroepiandrosterone sulfate in serum of newborn infants. It was found that with the mild-to-moderate form of pregnancy-induced hypertension (PIH), there was little effect on prolactin levels in newborn serum. In newborns of women with severe PIH, however, serum prolactin levels were significantly greater (p less than 0.01) than those in newborns of women with uncomplicated pregnancies. Conversely, umbilical serum concentrations of dehydroepiandrosterone sulfate in newborns of women with severe PIH were significantly less (p less than 0.05) than those in newborns of women with uncomplicated pregnancies. These findings are supportive of the view that pituitary function and adrenocortical function of fetuses of women with PIH are different from those of fetuses of normotensive women. These findings are suggestive that PIH alters the function of the fetal pituitary and adrenal cortex.

Adrenal Glands↗
PubMed1986

Relationship of age, sex, and reproductive status to the quantity of tyrosine hydroxylase in the median eminence and superior cervical ganglion of the rat.

Tyrosine hydroxylase (TH) in the median eminence (ME) and superior cervical ganglion (SCG) of the rat was quantified by means of an immunoblot procedure, using highly purified rat TH as the standard. Antibodies against rat TH were produced in the rabbit. The assay was linear from 0-100 ng TH and had a correlation coefficient of 0.990 +/- 0.0014 (mean +/- SE: n = 22). The interassay coefficient of variation was 8.65% (n = 17). In young female rats (12-16 weeks old) with regular 4-day estrous cycles, the quantity of TH in the ME on various days of the cycle was as follows: estrus, 42 +/- 2.9 ng; diestrous day 1, 61 +/- 2.8 ng; diestrous day 2, 75 +/- 4.2 ng; and proestrus, 84 +/- 3.3 ng. In ovariectomized rats (15-16 weeks old), the ME contained 24 +/- 1.6 ng TH. In prepubertal rats (5-5.5 weeks old), the ME of females contained 25 +/- 2.0 ng TH, and that of males contained 24 +/- 2.1 ng. The amount of TH in the ME of young mature males (15-16 weeks old) was 34 +/- 3.3 ng, and that of old males (17-20 months old) was 37 +/- 1.6 ng TH. In aged female rats (22-24 months old), the MEs of diestrous and estrous animals contained 71 +/- 2.8 and 63 +/- 4.2 ng TH, respectively. In cycling females (12-16 weeks old), the quantity of TH per SCG was as follows: estrus, 41 +/- 3.2 ng, diestrous day 1, 64 +/- 1.2 ng; diestrous day 2, 82 +/- 4.4 ng; and proestrus, 101 +/- 4.9 ng. In ovariectomized rats (15-16 weeks old), there was 34 +/- 2.0 ng TH/SCG. In prepubertal rats (5-5.5 weeks old), the SCG of females contained 33 +/- 4.1 ng TH, and that of males contained 32 +/- 2.3 ng. The amount of TH in SCG of mature males (15-16 weeks old) was 47 +/- 3.0 ng, and that in old males (17-20 months old) was 58 +/- 4.6 ng. In aged female rats (22-24 months old), the SCG of diestrous animals contained 152 +/- 6.3 ng TH, and that of constant estrous animals contained 139 +/- 8.8 ng TH. It is concluded that before puberty, the amounts of TH in the ME and SCG of female rats are similar to those in male rats. After puberty, the amount of TH in these structures is greater in females than in males.(ABSTRACT TRUNCATED AT 400 WORDS)

Age Factors↗
PubMed1985

Preparation and characterization of polyclonal and monoclonal antibodies against human aromatase cytochrome P-450 (P-450AROM), and their use in its purification.

Aromatase cytochrome P-450 (P-450AROM) was partially purified from human placental microsomes by hydrophobic affinity chromatography using Phenyl-Sepharose and ion-exchange chromatography on DEAE-cellulose. The resulting preparation had a specific activity of 2 nmol/mg protein with respect to cytochrome P-450 content and displayed a type I difference spectrum upon addition of the substrate androstenedione. When the cytochrome P-450-enriched fractions were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and stained with Coomassie blue, there was an enrichment of two proteins having apparent molecular weights of 50,000 and 55,000. The bands containing these proteins were removed from unstained polyacrylamide gels and injected separately or together into three rabbits. An aliquot of the serum or an immunoglobulin (IgG) fraction prepared from the serum of the rabbit injected with the 55-kDa band or with both the 50- and 55-kDa bands inhibited aromatase activity of human placental microsomes by 80%; this IgG had no effect on 17 alpha-hydroxylase or 21-hydroxylase activities of human fetal adrenal microsomes. In contrast, the serum of the rabbit injected with the 50-kDa band had little capacity to inhibit placental aromatase activity. By immunoblot analysis, it was found that the IgG from the serum of the rabbit immunized with the 55-kDa protein bound specifically to a protein of 55 kDa in human placental microsomes. Monoclonal antibodies were prepared from a hybridoma cell line derived from the spleen cells of mice immunized against the 55-kDa protein. The monoclonal IgG was covalently linked to a Sepharose 4B column and was used for immunoaffinity chromatography of cytochrome P-450AROM. The finding that cytochrome P-450 and the 55-kDa protein were selectively retained by the affinity column and eluted with NaCl (2 M) and glycine (0.2 M, pH 3.0) and that this fraction contained aromatase activity upon reconstitution with purified NADPH-cytochrome P-450 reductase and phospholipid, is indicative that the 55-kDa protein is indeed cytochrome P-450AROM. These findings are also indicative that both the monoclonal and polyclonal IgGs are specific for human cytochrome P-450AROM.

Animals↗
PubMed1985

Involvement of hypothalamic dopamine in the regulation of prolactin secretion.

The neuroendocrine control of prolactin (PRL) secretion is known to be a multifactorial process, but dopamine (DA) secreted by the tuberoinfundibular dopaminergic (TIDA) neurons of the hypothalamus is believed to exert a predominant inhibitory control on the secretion of PRL. The secretory activity of the TIDA neurons, including the rate of biosynthesis of DA and the rate of release of the neurohormone into hypophysial portal blood, can be readily evaluated in the rat. In most conditions in which an altered secretion of PRL has been documented, an altered secretory activity of the TIDA neurons has been found. When an acute reduction in the secretion of DA is observed, an increased secretion of PRL is associated, with an inverse relationship between DA and PRL concentrations in hypophysial portal and systemic blood, respectively. However, the secretion of PRL can be regulated by PRL itself through stimulation of the secretory activity of the TIDA neurons, and consequently hyperprolactinemia can be observed concomitantly with a sustained high secretion of DA, as seen after treatment with estrogen. The short loop feedback of PRL secretion seems to be impaired in the aging rat, since a sustained reduced hypothalamic secretion of DA is observed in spite of long-term hyperprolactinemia.

Aging↗
PubMed1984

Dopaminergic neurons in the mediobasal hypothalamus of old rats: evidence for decreased affinity of tyrosine hydroxylase for substrate and cofactor.

The effect of aging on the activity of tyrosine hydroxylase (TH) and on the number of TH-positive perikarya in the hypothalamus was studied in old and young female rats. The activity of TH in the mediobasal hypothalamus (MBH) of old rats was significantly (P less than 0.025) less than that in young rats. In old rats, the Km of TH for tyrosine as well as cofactor, 6-methyl-5,6,7,8-tetrahydropterine (6MPH4), was markedly greater than the Km in young rats. The maximal velocity was only slightly reduced in old animals. Contiguous coronal sections of the brain of an old and a young female rat were immunocytochemically stained for TH, and the TH-positive perikarya in the hypothalamus were counted. In the circumventricular region, 6793 TH-positive perikarya were present in the young brain and 6632 in the old brain. In the arcuate region, 2868 and 2760 TH-positive perikarya were counted in the young and old brain, respectively. It is concluded that the reduced TH activity in the MBH of old rats is not a consequence of a reduction in the number of TH-positive perikarya in the arcuate or circumventricular regions of the hypothalamus but is due to a reduction in the affinity of TH for its substrate and cofactor.

Age Factors↗
PubMed1984

Germ cell degeneration during postprophase of meiosis and serum concentrations of gonadotropins in young adult and older adult men.

Loss of potential sperm production during postprophase of meiosis was evaluated to determine if reduced daily sperm production in older men could be explained by an enhanced percentage of germ cell degeneration during this period of spermatogenesis. Evaluations were based on enumerating germ cells in homogenates of fixed testes using phase-contrast cytometry from 37 young adult (20-48 yr) and 34 older adult (50-85 yr) men. The time period in which germ cells degenerate was assessed in 10 men by comparing potential daily sperm production based on secondary spermatocytes with that based on primary spermatocytes or with daily sperm production based on spermatids. There was a significant (P less than 0.01) decline in sperm production potential based on primary spermatocytes and on spermatids in the older adult men such that the percentage of loss of potential production during postprophase was similar between the two age groups. Sperm production estimates based on primary spermatocytes and secondary spermatocytes were similar (P greater than 0.05); however, estimates based on secondary spermatocytes were significantly higher than those based on spermatids. Degeneration during postprophase of meiosis in humans appears to occur during or near the second meiotic division. Age-related reduced sperm production was significantly correlated with elevated levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Age-related decline in sperm production could not be explained by enhanced germ cell degeneration during postprophase but may result from reduced germ cell numbers prior to pachytene primary spermatocytes.

Adult↗
PubMed1984

Relationship between dopamine release into hypophysial portal blood and prolactin release after morphine treatment in rats.

To address the issue of whether, after morphine treatment, the reduced release of dopamine (DA) into portal blood is entirely responsible for the increased prolactin (PRL) release, the following study was conducted. The concentration of DA in plasma from a single portal vessel of untreated, ovariectomized rats was 1.85 +/- 0.33 ng/ml (mean +/- SE). Treatment of ovariectomized rats with alpha-methyl-p-tyrosine (alpha MT) caused a 91% reduction in the concentration of DA in portal plasma. Infusion of DA (0.4 microgram/min/kg BW) into a jugular vein of rats pretreated with alpha MT restored the DA concentration in portal plasma to that seen in untreated rats. Injection of morphine sulfate elicited a marked increase in the concentration of PRL in plasma. Infusion of DA at rates of 0.4 and 0.8 microgram/min/kg BW suppressed by 52 and 75%, respectively, the secretion of PRL after morphine treatment. Infusion of DA had no effect on the release of PRL induced by intracerebroventricularly administered beta-endorphin. Although treatment of rats with alpha MT caused release of PRL that was similar to that seen in rats treated with morphine, infusions of DA at 0.4 and 0.8 microgram/min/kg BW into alpha MT-treated, ovariectomized rats suppressed the secretion of PRL by 89 and 96%, respectively. Thus, after morphine treatment, the decreased release of DA into portal blood is not in itself sufficient to account for the increase seen in the secretion of PRL. It is suggested that morphine and opiate-like peptides induce the release of a hypothalamic substance(s) that stimulates PRL release.

Animals↗
PubMed1984

Evidence for alteration in the processing of dopamine in the anterior pituitary gland of aged rats: receptors and intracellular compartmentalization of dopamine.

Receptors for dopamine and the subcellular localization of dopamine in the anterior pituitary gland were studied in young cycling female rats and in aged, constant estrous female rats. Dopamine receptors were quantified in membrane preparations of anterior pituitary tissue using [3H] spiperone as the ligand. On the basis of saturation isotherms, it was calculated that the equilibrium dissociation constant (Kd) and binding capacity for [3H]spiperone binding to pituitary membranes from young rats were 34.2 pM and 82 fmol/mg protein, respectively. The relative binding capacity of membranes from aged rats was 35% greater than that of membranes from young rats. There was no difference in the Kd values in aged and young rats. When the relative binding of [3H]spiperone by anterior pituitary membranes from individual animals was quantified by incubation with a saturating concentration of the ligand, it was found that [3H]spiperone binding in aged rats was significantly greater than that in young rats. When the subcellular localization of dopamine in anterior pituitary tissue was examined by means of density gradient centrifugation, it was found that the subcellular distribution of dopamine in tissue of aged rats was quantitatively different from that in young rats. In young rats, a small amount of dopamine was associated with light particles, whereas a large amount of dopamine was associated with heavy particles, which cosedimented with PRL-containing granules. In aged rats, the amount of dopamine associated with light particles was 5 times that found in young rats, whereas the amount of dopamine associated with heavy particles was the same as that in young rats. We speculate that altered intracellular compartmentalization of dopamine, leading to a marked accumulation of dopamine in the light particles, is related to increased secretion of PRL in aged rats.

Aging↗
PubMed1984

Luteinizing hormone-releasing hormone and thyrotropin-releasing hormone in the hypothalamus of women: effects of age and reproductive status.

In the study of the effects of age and reproductive status on LHRH and TRH content in the hypothalamus of women, we found that the amount of LHRH (58 +/- 5.5 ng; mean +/- SE) in the hypothalamus of young women (16-29 yr) was significantly greater (P less than 0.001) than that (28 +/- 3.0 ng) in postmenopausal women (50-78 yr). The hypothalamic content of LHRH (18 +/- 2.4 ng) of bilaterally ovariectomized women (39-47 yr) was significantly less (P less than 0.001) than that (60 +/- 12.6 ng) in younger ovulatory women (30-39 yr) or that (56 +/- 13.5 ng) in ovulatory women of comparable age (40-49 yr). In contrast, the hypothalamic content of TRH (121.4 +/- 32.8 ng) in postmenopausal women were similar to that (122.3 +/- 12.5 ng) in young women. Although aging in women is associated with a significant reduction in the amount of LHRH in the hypothalamus, such a reduction appears to be a consequence of ovarian failure and not of aging per se.

Adolescent↗
PubMed1984

Leydig cell numbers, daily sperm production, and serum gonadotropin levels in aging men.

Age-related changes in Leydig cell number, daily sperm production, and circulating hormone levels were studied in 15 men between 20 and 48 yr of age and 15 men between 50 and 76 yr of age. Testes and blood samples were obtained at autopsy less than 15 h after death due to trauma or heart attack. Leydig cell number was determined by quantitative histometric estimation of the proportion of glutaraldehyde-perfused, decapsulated testicular parenchyma occupied by Leydig cell nuclei of measured average volume in both testes of each subject. Daily sperm production was determined by phase contrast cytometry of round spermatid nuclei in homogenates of both fixed testes from each individual. LH, FSH, PRL, and testosterone in serum from the heart or large veins were quantified by RIA. No relationship was detected between any of the testicular or hormonal values and postmortem time. The average total number of Leydig cells was reduced by 44% in the older men and was negatively correlated with age (p = -0.62) in all men. Mean serum LH was elevated more than 2-fold in the older men and was positively correlated with age (p = +0.53) in all men. Neither serum testosterone nor serum PRL changed significantly with age. Daily sperm production was more than 50% lower in older men and was negatively correlated with age (p = -0.76) in all men. Serum FSH was more than 3-fold higher in the older men and was positively correlated with age (p = +0.72) in all men. The highest FSH levels were found in men with the lowest rates of sperm production, and FSH and daily sperm production were inversely correlated even after the effects of age were removed. These findings show that the response of the human testis to aging is variable and that the predictive value of age for most testicular characteristics is weak at the level of individual men. Nevertheless, age accounts for more than a third of the variation in Leydig cell number, and it explains more than half the variation in daily sperm production. Hence, age is the largest single contributing factor yet identified in the search for explanations underlying the variation in testicular structure and function found in groups of normal men.

Adult↗
PubMed1984

A new clonal strain of rat pituitary tumour cells: a model for non-regulated secretion of prolactin.

A new clonal strain of Prl-secreting cells derived from the transplantable rat pituitary tumour, 7315a, has been established in culture. The cells of this strain, designed 235-1, have a highly developed Golgi complex, an extensive rough endoplasmic reticulum, and a few small but no large dense-core granules. When inoculated into athymic mice and rats of the Buffalo strain, the 235-1 cells produce tumours, and the host animals have hypertrophied mammary glands that produce milk, indicating that Prl secreted by these cells has mammotrophic activity. In monolayer culture, the doubling time of 235-1 cells is 31 +/- 1 h (mean +/- SE). The cells secrete Prl, a trace quantity of GH, but no LH, FSH, TSH, ACTH, or alpha-MSH. Prl is released at a rate of 257 +/- 12 fg per h per cell. The cellular content of Prl is 424 +/- 23 fg per cell. Prl secretion by 235-1 cells is not affected by dopaminergic agonists and antagonists, TRH, or oestradiol-17 beta but is inhibited in the presence of EGTA or monensin, an ionophore that is believed to act at the level of the Golgi complex. The subcellular distribution of Prl in 235-1 cells is different from that in rat pituitary cells. In 235-1 cells, Prl is associated not with a single set of dense particles as it is in pituitary cells but with 2 sets of subcellular particles, of which 1 set cosedimented with particles having lysosomal enzyme activity. These findings suggest that Prl secretion by 235-1 cells involves secretory pathways that are different from those seen in normal lactotrophs.

Animals↗
PubMed1983

An inhibitory role for morphine on the release of dopamine into hypophysial portal blood and on the synthesis of dopamine in tuberoinfundibular neurons.

The intracerebroventricular administration of morphine to ovariectomized rats resulted in a marked decrease in the concentration of dopamine in plasma of hypophysial portal blood. A 90% reduction in the rate of release of hypothalamic dopamine into hypophysial portal blood occurred during the 60 min following the intraventricular administration of 60 ng of morphine sulfate. A dose-related decrease in the rate of release of dopamine into the portal vasculature was observed between 7.5 ng and 60 ng of morphine sulfate. Regardless of the quantity of morphine sulfate (1-500 ng) given to the animals, the concentrations of norepinephrine and epinephrine in hypophysial portal plasma and femoral arterial plasma remained unchanged. The efficacy of morphine on the release of dopamine into hypophysial portal blood was not associated with an equal efficacy of the drug on the synthesis of dopamine in tuberoinfundibular neurons, as evaluated by the accumulation of dihydroxyphenylalanine (DOPA) in the median eminence of rats given 3-hydroxybenzylhydrazine (NSD 1015). No effect of morphine was observed on DOPA accumulation in the median eminence of NSD-treated rats that had received 50 ng of morphine sulfate intracerebroventricularly, and only a 50% reduction was observed in the accumulation of DOPA in the median eminence of rats given 500 ng of morphine sulfate. These findings are supportive of the view that morphine inhibits both the release and synthesis of dopamine but is more effective in inhibiting the release than synthesis of dopamine.

Animals↗
PubMed1983

Regional localization and subcellular compartmentalization of thyrotropin-releasing hormone in adult human brain.

In the current study, we sought to define the subcellular compartmentalization of thyrotropin-releasing hormone (TRH) in adult human brain tissues. Upon evaluating tissues (3-24 h post mortem) from 62 humans, ranging in age from 5 to 75 years, we found that TRH was widely distributed throughout the brain. The highest TRH concentration (ng/mg protein) was in the stalk-median eminence region of the hypothalamus (19.3 +/- 3.3, mean +/- SE); the TRH concentration in the hypothalamus, exclusive of the stalk-median eminence, was much lower (1.7 +/- 0.2). Substantial quantities of TRH also were detected in the medulla oblongata (0.26 +/- 0.08), mammillary bodies (0.33 +/- 0.25), and optic chiasm (0.14 +/- 0.07). Lower levels of TRH were found in the amygdala (0.060 +/- 0.015) and the corpus striatum (0.033 +/- 0.010). TRH was near or below the limits of detection in tissues of the cerebral and cerebellar cortices, the olfactory bulbs, the pons, and the hippocampus. When homogenates of medial basal hypothalamic tissue (prepared in 0.32 M sucrose-10 microM CaCl2) were fractionated by means of differential centrifugation, most of the TRH was recovered in subcellular particles which were pelleted at 10,000 X g and which contained the highest amounts of occluded LDH activity. When the nuclei-free supernatant fluid (900 X g S) was fractionated on discontinuous sucrose density gradients or continuous sucrose density gradients, most of the TRH was recovered in subcellular fractions containing synaptosomes. The subcellular distribution of TRH appeared to be stable for up to 24 h post mortem in rat and human brain tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1983

Cardiovascular effects and clearance of arginine vasopressin in the fetal lamb.

Increased fetal secretion of arginine vasopressin (AVP) occurs in association with complicated pregnancies, asphyxia, and meconium-stained amniotic fluid (AF); yet, the role of AVP in fetal homeostasis remains unclear. Using chronically instrumented, near-term lamb fetuses (n = 8), we have ascertained the cardiovascular responses to doses of AVP ranging from 1.94 to 8.73 mU/min, the clearance of AVP from plasma, and the occurrence of meconium release into AF during AVP infusions. AVP administration resulted in a dose-related rise in arterial pressure; although heart rate fell, the decline was not dose-related and occurred before the pressor response. Clearance of plasma AVP was 60 +/- 8.7 ml X kg-1 X min-1, and the half-time in plasma was 2.8 min. AVP was not cleared across the fetal placenta nor by fetal-maternal transport. However, the AF concentration of AVP rose fourfold after the infusion of AVP was stopped. Meconium release into AF occurred in fetuses infused with AVP at rates greater than or equal to 7.76 mU/min. AVP has hemodynamic effects that mimic fetal responses to intrauterine "stress" and may be causally associated with the fetal release of meconium into AF. Furthermore, plasma AVP is cleared in part by the fetal kidney.

Amniotic Fluid↗