Prolactin action on extracellular fluid volume in tails of stage XII bullfrog tadpoles

Hormonal effect on the osmotic, electrolyte and nitrogen balance in terrestrial Amphibia

Two main hormones regulate water balance in amphibian. First, mesotocin (MT) acting as a diuretic agent, and second arginine vasotocin (AVT) being an anti-diuretic hormone. In addition, prolactin (PRL), aldosterone, corticosterone, angiotensin II and atriunatriuretic hormones, play a role too in regulating water and ion balance. The hormones affect the epidermis and bladder permeability to water and ions as well as the kidney through the control of the glomerular filtration rate (GFR). The main questions concern the presence and action of these hormones during the amphibian's life history. Are they present in both larval and adult stages? Are these hormones being synthesized in both aquatic and terrestrial adult phases? Under what circumstances are they being stored or released? Would the target organs (epidermis, bladder, kidney) respond in a similar way during all periods? The problem is the fact that under most circumstances an amphibian while in an aquatic environment responds physiologically differently than when on land. Only partial information concerning hormone presence, release and control of water balance is available at the moment, and even that is fragmentary and based on only a very small number of amphibian species.

Osmoregulatory effects of prolactin and growth hormone in embryonic chicks

Intact White Leghorn chick embryos were treated daily (on Days 6-13) with bovine prolactin (PRL) or ovine growth hormone (GH) at doses of 4-10 micrograms/g embryo wet wt. A control group received an equal volume of avian saline. [Na+] and [Cl-] were determined in allantoic fluid samples taken on Days 10, 12, and 14, and in amniotic fluid and blood plasma on Day 14. Allantoic fluid, amniotic fluid, and plasma osmolarities, embryo wet weight, hematocrit, and allantoic fluid volume were also determined on Day 14. PRL-treated embryos showed significantly lower allantoic [Na+] and [Cl-] compared to controls at Days 10, 12, and 14. Allantoic fluid osmolarity was reduced, and plasma osmolarity increased, at Day 14 in PRL-treated embryos. By contrast, PRL had no effect on allantoic volume, amniotic fluid [Na+], [Cl-], or osmolarity, plasma [Na+] or [Cl-], hematocrit, or embryo wet weight. GH-treated embryos showed significantly reduced allantoic [Na+] at both Days 10 and 14, but no other treatment effect. Calculations show that the decrease in total allantoic Na+ seen in PRL-treated embryos is equivalent in magnitude to 10% of the total egg Na+. Results from studies on embryonic amphibians and mammals suggest that this sodium is likely to be sequestered in an expanded extracellular volume.

Breeding condition, temperature, and the regulation of salt and water by pituitary hormones in the red-spotted newt, Notophthalmus viridescens

In vivo integumental transepithelial potential (TEP) in the Eastern red-spotted newt (Notophthalmus viridescens) increases linearly with external [Na+] from 0.1 to 10 mM and is anion independent. Both integumental TEP and osmotic permeability are higher in laboratory-conditioned (LC, terrestrial) than in breeding-condition (BC, aquatic) newts at temperatures of 5-25 degrees. Prolactin (PRL) treatment of LC newts decreased both TEP and rate of water uptake. Arginine vasotocin (AVT) treatment resulted in a substantial increase in water uptake in LC newts, while little or no AVT response was seen in PRL-treated or BC newts. Hypophysectomy (HX) or ergocryptine treatment increased TEP in BC newts, whereas HX + PRL maintained TEP at control levels. Although ergocryptine and HX were without effect on water uptake in BC newts kept at 5 degrees for 9 days, HX + ACTH increased water uptake. HX produced a substantial fall in serum [Na+] in BC newts, while either PRL or ACTH replacement elevated serum [Na+]. Combined ACTH and PRL treatment returned serum [Na+] to control levels. These data suggest that high endogenous prolactin plays a significant role in maintaining serum [Na+] and integumental permeability and transport characteristics in breeding-condition N. viridescens. Although PRL and ACTH are both sodium retaining in the aquatic breeding stage, these two hormones promote opposite effects on the integument; PRL decreases both water uptake and integumental TEP, whereas ACTH (presumably acting through the adrenals) increases water uptake and possibly TEP.