Correction of hemorrhage-induced anemia with intra-amniotic iron in the ovine fetus.

OBJECTIVE: This study tested the hypothesis that intra-amniotic iron treatment would enhance fetal red blood cell production after an acute, severe fetal hemorrhage of 40% of estimated blood volume over 2 hours. STUDY DESIGN: Three groups of late-gestation ovine fetuses were studied for 10 days: (1) control fetuses (n = 8), (2) fetuses hemorrhaged on day 3 (n = 11), and (3) similarly hemorrhaged fetuses supplemented with a single bolus of 60 mg of iron injected intra-amniotically immediately after the hemorrhage (n = 7). Statistical analysis was by 3-factor analysis of variance. RESULTS: At 24 hours after hemorrhage, red blood cell mass increased 5% in the control group and was reduced equally in both hemorrhage groups by 32% below day 3 prehemorrhage values. At 7 days after hemorrhage, red blood cell mass increased 27.8% +/- 2.6% (SE) above day 3 baseline values in the control fetuses. In the nonsupplemented hemorrhaged fetuses, red blood cell mass was not different from prehemorrhage values after 7 days (+3.7% +/- 4.1%), whereas red blood cell mass increased by 29.9% +/- 6.1% above prehemorrhage values in the iron-supplemented hemorrhage group (P <.001). CONCLUSION: Intra-amniotic iron supplementation resulted in full restoration of red blood cell mass within 7 days after a large loss of blood in fetal sheep, whereas restoration failed without iron supplementation. Intra-amniotic iron treatment may be of therapeutic value in restoring red blood cell mass in human fetuses with certain types of anemia such as that resulting from fetal or fetomaternal hemorrhage.

Role of endogenous atrial natriuretic factor in the regulation of fetal cardiovascular and renal function.

The purpose of the present study was to determine whether endogenous atrial natriuretic factor participates in the maintenance of normal vascular pressure and renal function in ovine fetuses at 128 to 130 days' gestation. Circulating atrial natriuretic factor in the fetus was immunoneutralized by an intravenous bolus injection of an atrial natriuretic factor antiserum at a dilution of 1:2000 (low dose, n = 7) or 1:400 (high dose, n = 6). In the high-dose group, plasma atrial natriuretic factor concentration was significantly reduced by 65 +/- 14 pg/ml from basal levels of 165 +/- 12 pg/ml within 10 minutes and remained reduced for the 90-minute period after the injection. Fetal arterial pressure acutely and transiently decreased, but at 50 minutes arterial pressure increased and was elevated for the remainder of the experiment. Urine flow and urinary excretion rates of sodium, potassium, and chloride were reduced within 10 minutes after the injection. Urine flow rate was suppressed for as long as plasma atrial natriuretic factor concentrations were reduced. Fetuses in the low-dose and control groups showed no significant change in cardiovascular or renal function. In response to atrial natriuretic factor antiserum injection, plasma angiotensin II concentrations were increased, whereas plasma arginine vasopressin concentrations were unchanged. These results suggest that endogenous atrial natriuretic factor is involved in the maintenance of arterial pressure and urinary excretion in the ovine fetus.

Mammotroph and gonadotroph volume percentage in the rat anterior pituitary after lesions of the medial basal hypothalamus.

A lesion of the medial basal hypothalamus (MBH) results in enhanced secretion of prolactin and reduced release of the other hormones from the anterior pituitary. We measured the volume percentage of the prolactin-secreting mammotrophs, stained immunocytochemically, under several experimental conditions to assess the morphological correlated of the high secretion of prolactin. In addition, gonadotrophs were stained both tinctorially with the periodic acid-Schiff reagent and immunocytochemically with antibodies to luteinizing hormone. Anterior pituitaries were studied from female rats which were: (1) cycling, (2) ovariectomized for 2 weeks, (3) ovariectomized for 2 weeks with a lesion of the MBH for 1, 14 and 21 days. The volume percentage of mammotrophs and gonadotrophs in the lateral, central and middle fields of the anterior pituitary was determined and this measurement was expressed relative to endocrine cellular area so that vascular space and necrotic regions would not be included in the assessment. Ovariectomy significantly decreased mammotroph and increased gonadotroph volume percentage when compared to the intact animals. MBH lesions had the opposite effect. At 14 and 21 days after a lesion, the volume percentage of mammotrophs was significantly greater than in the intact rat, while the volume percentage of gonadotrophs was identical to that observed in the intact rat. These data suggest that the elimination of the prolactin-inhibitory hormone(s) of the MBH result in hypertrophy and/or hyperplasia of mammotrophs. This effect occurs in the absence of ovarian and may be of importance in the induction of prolactin-secreting pituitary adenomas. The data also support the hypothesis that destruction of gonadotropin-releasing hormone neuron terminals countermands the hypertrophy of gonadotrophs induced by ovariectomy.

Stimulation of prolactin secretion by neuroleptics in rats with medial basal hypothalamic lesions.

The ability of dopamine receptor antagonists to stimulate prolactin release in rats with medial basal hypothalamic lesions was investigated. Starting levels of prolactin were elevated to approximately 400 ng/ml in animals in which the tuberoinfundibular dopaminergic neurons were completely destroyed by the lesion. In lesioned animals, chlorpromazine administration at doses of 0.1 and 5 mg/kg induced a further 2- to 3-fold significant increase in plasma prolactin levels. the incubation of anterior pituitaries from lesioned animals with 10(6) M chlorpromazine had no effect on prolactin secretion, thereby eliminating the possibility that chlorpromazine itself stimulates prolactin release from the anterior pituitary. A similar increase in plasma prolactin in lesioned rats was also observed with the potent dopamine antagonist d-butaclamol (1 mg/kg). The effect was stereospecific since the inactive isomer l-butaclamol did not produce any change in the circulating levels of prolactin. Pimozide, another dopaminergic antagonist, was ineffective in inducing a further increase in prolactin in lesioned rats when 0.63 mg/kg was used. However, at a 10-fold lower concentration (0.63 mg/kg), pimozide stimulated a significant increase in prolactin in lesioned rats. The involvement of an alpha-adrenergic mechanism was ruled out by the inability of phentolamine (2.5 mg/kg) to increase prolactin secretion. These data suggest that dopaminergic antagonists can further increase prolactin levels in medial basal hypothalamus-lesioned rats possibly by blocking the inhibitory action of dopamine from nonhypothalamic sources, or by releasing a substance which possesses prolactin-releasing activity.

Increased responsiveness of the dopamine-mediated inhibition of prolactin synthesis after destruction of the medial basal hypothalamus.

Long term destruction of the tuberoinfundibular dopaminergic neurons results in increased responsiveness of the anterior pituitary to the suppression of PRL release by dopamine. In the present study we tested whether long term destruction of these neurons by medial basal hypothalamic lesions would also increase the potency of dopamine in suppressing the release and apparent synthesis of PRL. Anterior pituitaries from ovariectomized control rats and ovariectomized rats lesioned for 2 weeks were incubated for 3 h in medium 199 containing [3H]leucine in the presence or absence of various concentrations of dopamine. Labeled PRL was separated by polyacrylamide gel electrophoresis and quantitated by liquid scintillation spectroscopy. Concentrations of dopamine ranging from 10(-8)-10(-6) M caused a dose-dependent suppression of labeled newly synthesized PRL released into the medium from anterior pituitaries of medial basal hypothalamus-lesioned animals. With pituitaries from the nonlesioned rats, newly synthesized PRL release was progressively inhibited by 10(-7) and 10(-6) M dopamine, while 10(-8) M dopamine actually significantly stimulated PRL release. Total labeled PRL (that released and that remaining in the gland) was equally suppressed by all three concentrations of dopamine in pituitaries from lesioned animals, but only a minor effect was observed at the highest concentration of dopamine with the control pituitaries. Therefore, the potency of dopamine to suppress the release and apparent synthesis (total labeled PRL) of newly synthesized PRL from pituitaries of long term lesioned animals was increased.

Effects of testosterone implants and hypothalamic lesions on luteinizing hormone regulation in the castrated male rat.

The effects of intrahypothalamic and subcutaneous implants of testosterone (T) and those of hypothalamic lesions on resting levels of circulating LH and pituitary responsiveness to exogenous LHRH were studied in castrated male rats to elucidate hypothalamic and pituitary regulation of LH secretion. Two hundred mug implants of testosterone propionate (TP) in the median eminence region suppressed plasma LH titers before evidence of direct inhibition of pituitary function (as indicated by testing with LHRH) was found. Such implants release appreciable amounts of T into the peripheral circulation in the immediate post-operative period, and SC Silastic (constant release) capsules containing T have similar effects. The findings suggest that, regardless of the site of implant, the initial negative feedback inhibition of LH by T is not dependent on direct action at the pituitary levels but rather appears to be a hypothalamic effect. In the days following exposure to hypothalamic or peripheral implantation of T, however, a progressively developing decline in the response to exogenous LHRH was observed. In order to determine whether this effect results from suppression of endogenous LHRH release, the median eminence-arcuate region was destroyed to remove the source of LHRH. In these animals, the suppression of plasma LH was evident on the first day after the lesion, but pituitary responsiveness to LHRH was unaffected until after one week. When Sialastic capsules were implanted SC into lesioned animals, a more rapid (less than 1 week) inhibition of pituitary responsivity ensued. Suprachiasmatic lesions did not affect basal LH secretion or pituitary responses to LHRH. The data provide evidence for a dual feedback action of T on LH in castrated male rats: an initial inhibitory effect presumably due to hypothalamic inhibition (commencing at around 6h after hypothalamic of SC implantation of T), and a subsequent suppression of pituitary responisveness (after one day) presumably due to direct action of T on the pituitary. In addition to these phenomena, findings in rats bearing median eminence-arcurate lesions suggest that the removal of endogenous LHRH by itself leads to an eventual decline in pituitary responsiveness (greater than one week postoperatively).

Supersensitivity of anterior pituitary dopamine receptors involved in the inhibition of prolactin secretion following destruction of the medial basal hypothalamus.

The medial basal hypothalamus of ovariectomized rats was destroyed using a modified Halász knife. Large increases in prolactin secretion were observed 1 and 14 days following the lesions. Long- and short-term lesioned animals were anesthetized with chloral hydrate and treated with various doses of apomorphine (0.05, 0.2, 2, 5 mg/kg). Blood samples were obtained before and 10, 30 and 60 minutes after the injection. Both the 0.05 and 0.2 mg/kg doses caused significantly greater and longer-lasting inhibition of prolactin in long-term than in short-term lesioned animals. Since the MBH was totally destroyed this study suggests that anterior pituitary dopamine receptors involved in the inhibition of prolactin secretion become supersensitive in long-term lesioned rats.