THE NEUROHYPOPHYSIAL HORMONES OF LUNGFISHES AND AMPHIBIANS

Seahorse Male Pregnancy as a Model System to Study Pregnancy, Immune Adaptations, and Environmental Effects

Seahorses, together with sea dragons and pipefishes, belong to the Syngnathidae family of teleost fishes. Seahorses and other Syngnathidae species have a very peculiar feature: male pregnancy. Among different species, there is a gradation of paternal involvement in carrying for the offspring, from a simple attachment of the eggs to the skin surface, through various degrees of egg coverage by skin flaps, to the internal pregnancy within a brood pouch, which resembles mammalian uterus with the placenta. Because of the gradation of parental involvement and similarities to mammalian pregnancy, seahorses are a great model to study the evolution of pregnancy and the immunologic, metabolic, cellular, and molecular processes of pregnancy and embryo development. Seahorses are also very useful for studying the effects of pollutants and environmental changes on pregnancy, embryo development, and offspring fitness. We describe here the characteristics of seahorse male pregnancy, its regulatory mechanisms, the development of immune tolerance of the parent toward the allogeneic embryos, and the effects of environmental pollutants on pregnancy and embryo development.

Renal responses to mesotocin in Western painted turtles compared with the antidiuretic response to arginine vasotocin

We have examined the renal responses to the two neurohypophysial peptides mesotocin (MT) and arginine vasotocin (AVT) in Western painted turtles (Chrysemis picta). Ureteral urine was collected, after removal of the urinary bladder, to exclude modification by trans-bladder fluxes of ions and or water. Test doses of MT ranged from 5 to 500 ng kg(-1) i.v. but only the uppermost pharmacological doses of 300 and 500 ng kg(-1) were followed by even a small reduction in GFR, a renal tubular antidiuresis, and a decrease in percent relative free-water one word clearance. A much lower, physiological, dose of 5 ng kg(-1) of AVT attenuated significantly the GFR for 30 min and decreased the percent relative free-water clearance until the end of a 150 min observation period. This is the first report of the renal response to MT in a reptile. It was concluded that MT is not a diuretic hormone, as it is in amphibians and that AVT may be the naturally occurring antidiuretic hormone in the Chelonians.

Effect of salt depletion on sodium concentration in serum and urine of Bufo chilensis. Evidences for increased levels of neurohypophysial principles in their plasma

Salt-depleted toads Bufo chilensis were compared with animals maintained in NaCl solution and a control group with respect to Na+ content in serum and urine. Plasma hydro-osmotic activity of the animals was measured by increased water transfer across the isolated urinary bladder of the frog (Caudiverbera caudiverbera). Sodium in serum is not affected by pre-adaptation in distilled water. Urine Na+ is markedly reduced. Plasma from depleted animals increases water transfer across the isolated urinary bladder. Immersion in NaCl solution did not have this effect. An increase in neurohypophysial hormones in the blood of the animals is postulated.

The nonmammalian-mammalian transition through neurohypophysial peptides

Neurohypophysial hormones are particularly proper evolutionary tracers. Whereas Eutherian mammals have oxytocin and virtually always arginine vasopressin, nonmammalian tetrapods possess instead mesotocin and vasotocin. The transitions of mesotocin-oxytocin and vasotocin-vasopressin involved in the passage of reptiles-mammals seem to have occurred independently. Australian marsupials are endowed with mesotocin but American marsupials have either oxytocin (South-American opossums) or both oxytocin and mesotocin (North-American opossum). These results suggest that Australian Metatherians have preserved reptilian mesotocin and used it for milk-ejecting function whereas the change mesotocin-oxytocin appeared only in the American line. All marsupials have either arginine vasopressin or lysipressin and phenypressin (Australians) or lysipressin and arginine vasopressin (Americans). It is assumed that the change of vasotocin into arginine vasopressin occurred very early, perhaps in mammal-like reptiles, and duplication of the gene with subsequent mutations has led to the presence of two vasopressin-like peptides in most Metatherians.

The permeability of the skin of a neotenous urodele amphibian, the mudpuppy Necturus maculosus

1. The permeability of the isolated skin of a neotenous urodele amphibian, the mudpuppy Necturus maculosus, to Na, Cl, urea and water was measured. 2. Unidirectional transcutaneous flux measurements and the action of ouabain and amiloride, showed that there was normally no active Cl or Na transport, nor a Cl/Cl exchange diffusion process. 3. Amphotericin B initiated a transcutaneous potential difference and short-circuit current, which could be inhibited by ouabain. 4. The short-circuit current was nearly equivalent to the net Na Transport and this was also inhibited by ouabain. 5. A transcutaneous active Na transport mechanism thus appears to be incipient in the mudpuppy but is limited by a low permeability of the outer barrier of the cells. 6. Vasotocin increased the skin's diffusion permeability for water but had no effect on the influx of Na or urea. 7. The function of Necturus skin is in several respects unique compared to that of other amphibians.

Water uptake by the crab-eating frog Rana cancrivora, as affected by osmotic gradients and by neurohypophysial hormones

1. The rate of water uptake across the skin was investigated in live Rana cancrivora, an euryhaline frog which has been reported to tolerate sea water. When they were exposed to distilled water at 29 degrees C, the rate of water uptake was 8.4 +/- 0.4 mul./cm(2).hr; when bathed in solutions ranging from 30 to 570 m-osmole/l., irrespective of whether the solute was sucrose, urea or NaCl, the rate of fluid uptake during the first day was inversely related to the osmolarity of the solution. No appreciable fluid movement was observed when the bathing solution had an osmolar concentration of 270 m-osmole/l.2. The rate of fluid uptake was not affected by injections of vasopressin, oxytocin or of extracts of amphibian or rat pituitary glands, irrespective of whether R. cancrivora were bathed in distilled water or in solutions of NaCl or sucrose.3. In Bufo melanostictus, in contrast with R. cancrivora, injections of neurohypophysial extracts produced a marked increase of the rate of fluid uptake.4. In the laboratory, R. cancrivora could be acclimatized stepwise to tolerate NaCl solutions up to 700 m-osmole/l. for 7 days.5. After 24 hr exposure either to distilled water or to NaCl solutions from 100 to 670 m-osmole/l., the osmolar concentration of the plasma of R. cancrivora was always higher than that of the bathing fluid. In R. pipiens or R. temporaria plasma osmolar concentration was higher than that of the bathing fluid only when the latter did not exceed 300 m-osmole/l.6. Under all conditions investigated, the osmolar concentration of the urine of R. cancrivora was always lower than that of the plasma.7. The amounts of pressor and oxytocic activities of pituitary glands of R. cancrivora kept in distilled water or in NaCl solutions up to 300 m-osmole/l. were 8.9 +/- 0.8 and 1.8 +/- 0.3 m-u./gland, irrespective of sex or body weight within the range 30-50 g. After 3 days exposure to hypertonic NaCl solutions, the amounts of pressor and oxytocic activities were 14.7 +/- 1.2 and 3.1 +/- 0.3 m-u./gland. In both instances the pressor/oxytocic ratio was 4.9. Pituitary glands of R. temporaria similarly showed increased pressor and oxytocic activities after exposure to NaCl solutions of 300-360 m-osmole/l.