PROLACTIN HOMEOSTASIS IN VLBW INFANTS: EFFECT OF HYPOCALCEMIA (HC) AND CA INFUSION ON PROLACTIN RELEASE AND SECRETION IN NEONATES

Abstract

In vitro, prolactin secretion but not release is influenced by media Ca. Prolactin homeostasis in VLBW infants and effect of neonatal HC on secretion and release of prolactin are unclear. In 6 preterm AGA neonates, birthwt. 1050 ± 96 gms(mean ± sd), gestation < 32 wks, we studied the theses: 1)serum prolactin would be high; 2)serum Ca <6.0 mg/dl would be associated with decline in serum prolactin; 3)Ca infusion would not affect prolactin release; but may increase prolactin secretion. Serum Ca, iCa, Mg, P, and prolactin were determined on entry; when serum Ca <6.0 mg/dl; immediately post infusion of 18 mg/kg of Ca as 10% Ca gluconate over 10 minutes; +8 hrs post Ca infusion. Serum prolactin was determined by RIA (N <18 ng/ml in males, < 25 ng/ml in females). Serum total Ca was 7.4 ±0.2 at 11 ± 2.6 hrs of age, and declined to 5.1 ±0.2 mg/dl (mean ± se,p <0.025) at 46 ±9 hrs and rose to 9.2 ± 0.7 and 7.1 ± 0.5 mg/dl immediately and +8 hrs post Ca infusion; serum iCa was 5.24 ± 0.3, 3.8 ± 0.2, 6.9 ± 0.6 and 4.2 ± 0.2 mg/dl at these times, serum Mg and P did not change. Basal serum prolactin was elevated 209 ±41 ng/ml (p <0.05 vs adult control) and declined to 121 ± 23 ng/ml, p < 0.05, associated with hypocalcemia; immediately post Ca serum prolactin was 124 ± 28 ng/ml and 129 ± 20 ng/ml at +8 hrs post Ca. Thus, in VLBW infants, 1) serum prolactin is extremely high; 2) serum prolactin declines postnatally associated with decline in serum Ca low as 5.0 mg/dl; 3)in HC Ca infusion does not cause acute or subacute changes in serum prolactin. We speculate that although serum Ca and prolactin show similar temporal changes, serum Ca, low as 5.0 mg/dl with low serum iCa does not modify prolactin homeostasis.