Peter K.T. Pang

Prolactin and pituitary control of calcium regulation in the killifish, Fundulus heteroclitus

Abstract Hypophysectomized killifish ( Fundulus heteroclitus ) adapted to calcium-deficient seawater showed significant decreases in plasma calcium levels 8 days after the operation. At Day 16, plasma calcium levels were no longer significantly different from those of operated control fish. Plasma sodium and potassium levels were unaffected at all time periods. Injections of whole carp ( Cyprinus carpio ) pituitary homogenate corrected the hypocalcemia seen in the hypophysectomized killifish. When the carp glands were divided into “anterior”, “middle”, and “posterior” portions and tested in the hypocalcemic fish, the “middle” portion had the greatest corrective effect. Histological studies demonstrated that this portion probably contains the largest number of prolactin cells. In all cases, plasma sodium levels were elevated. In one experiment, a prolactin cell-free “posterior” portion had no hypercalcemic or hypernatremic effect. Injections of prolactin produced a log-dose-related hypercalcemia and hypernatremia in the hypophysectomized killifish. The highest dose of prolactin used (10 μg/g of body wt per injection) had a reduced hypercalcemic effect. Based on all these data, we suggest that prolactin may be the pituitary hypercalcemic principle in the killifish.

Effects of Synthetic Parathyroid Hormone on Vascular Beds of Dogs

Blood flow rates and vascular resistance in dogs were determined in 14 tissues with 15 +/- 2 microns radioactive microspheres (141Ce, 51Cr, 85Sr). Intravenous injections of synthetic bovine parathyroid hormone containing the NH2-terminal 1--34 amino acids [bPTH-(1--34)] at the dose of 10 USP units/kg body weight produced hypotension and increases in blood flow rate and decreases in resistance in kidney cortex, kidney medulla, heart, liver, stomach and pancreas at 1/2 and 2 min after injection. 4 U bPTH-(1--34)/kg body weight produced less vasodilation. Saline injection had no effect on the tissues studied.

Renal responses of the Chilean toad, Calyptocephalella caudiverbera, and the mud puppy, Necturus maculosus, to mesotocin

Abstract Intravenous injections of mesotocin resulted in increased urine production in the Chilean toad, Calyptocephalella caudiverbera , and the mud puppy, Necturus maculosus . At low doses, the diuretic responses increase with the doses of hormone administered, but at high doses the diuretic response is considerably reduced. These findings confirm those reported previously for the bullfrog ( P.K.T. Pang and W.H. Sawyer, 1978 , Amer. J. Physiol. 235 (2), F151–F155). However, this is the first time that such data are reported for an aquatic toad and an aquatic urodele.

Effects of sex steroids on plasma calcium levels in male killifish, Fundulus heteroclitus

Abstract Injection of 0.5 or 2 μg of estradiol benzoate/g of body wt produced hypercalcemia in male killifish while injection of the same doses of testosterone proprionate had no effect on plasma calcium levels. Injection of these sex steroids had no consistent effect on hepatosomatic index, gonadosomatic index, percentage hematocrit, or water, sodium, or potassium content of muscle.

Cardiac actions of bovine parthhyroid hormone fragment (1–34) in some lower vertebrates

Only recently have the cardiac actions of parathyroid hormone and its N-terminal (1-34) fragment (bPTH(1-34] been examined. Parathyroid hormone was found to exert a positive chronotropic effect on the heart tissue of several mammals and one amphibian in vivo and/or in vitro. The purpose of the present study was to examine in vitro the heart tissue of several lower vertebrates, particularly aquatic vertebrates, for responsiveness to bPTH(1-34) and, for comparative purposes, isoproterenol. Heart tissue (atrium or the entire heart) from all the animals studied (trout, mudpuppy, bullfrog tadpole, and adult bullfrog) responded to isoproterenol in a dose-dependent fashion with increased heart rate and contractile force. Only the atria from the adult bullfrog, however, responded in a similar manner to the administration of bPTH(1-34). In all cases propranalol (10(-6) M) was able to block both chronotropic and inotropic effects of isoproterenol but had no effect on the cardiac stimulation induced by bPTH(1-34) in the adult bullfrog atrium. The data suggests that cardiac responsiveness to bPTH(1-34) is associated with a terrestrial as opposed to an aquatic existence.

Comparative study on the cardiac actions of bovine parathyroid hormone (1–34)

The cardiac stimulatory effects of bovine parathyroid hormone (1-34) [bPTH-(1-34)] were studied on isolated atria and ventricular strips from cobra snakes (Naja naja), ducklings (Anas platyrhynchos), pigeons (Columba livia), Japanese quails (Coturnix coturnix japonica), laboratory rats (Rattus norvegicus), and dogs (Canis familiaris). In all atrial preparations, bPTH-(1-34) caused positive chronotropism. This suggests that the chronotropic effect of PTH is ubiquitous among the terrestrial vertebrates. Only the atria of cobra snakes and ducklings gave positive inotropic responses to PTH. No ventricular preparations showed significant response to bPTH-(1-34). This suggests the absence of cardiac stimulatory PTH receptors in the ventricles. Dog papillary muscle, however, showed slight but significant responses to bPTH-(1-34). The reason for this discrepancy between the responses of papillary muscles and the ventricular strips to PTH is unknown.