Charles S. Nicoll

The comparative endocrinology of prolactin.

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Prolactin and tadpole growth.

Summary Mammalian prolactin inhibits thyroxin-induced resorption of the tail in Rana catesbeiana tadpoles. Mammalian growth hormone does not show this effect. The possible importance of prolactin as a larval growth hormone in amphibians is emphasized.

Evolutionary biology of prolactins and somatotropins II. Electrophoretic comparison of tetrapod somatotropins

Proteins of the adenohypophyses of representatives of all four classes of tetrapods were separated by polyacrylamide disc gel electrophoresis. These were tested for somatotropic activity in the toad, Bufo boreas, using increases in linear growth as the criterion for somatotropic activity. In all species examined, somatotropic activity was associated with prominent, slow-migrating adenohypophysial proteins. However, some prolactins also exhibit somatotropic activity. Ovine and bovine prolactins (NIH) had somatotropic activity that cannot be accounted for by growth hormone contamination: these prolactins are considerably less potent than mammalian growth hormone. In two turtles, Pseudemys scripta and Chrysemys picta, proteins which previously had been identified as prolactins were as potent as growth hormones with respect to their somatotropic activity in the Bufo. Thus, these chelonians contained two distinct and prominent adenohypophysial proteins with somatotropic activity. Prolactin from a toad (Bufo marinus) may also have somatotropic activity but is less potent than the homologous growth hormone. Our results clearly indicate that in all tetrapod species examined, prolactins and somatotropins are separate molecular entities, the prolactin always having the higher electrophoretic mobility. However, the results with the turtles, toad, and with purified ovine and bovine prolactin indicate that, as in primates, adenohypophysial proteins may have both prolactin and somatotropic activities. Human placental lactogen (=chorionic somatomammotropin) was ineffective in the toad growth test. Estimation of the concentration of prolactin and growth hormone in adenohyphphyses by densitometry revealed that mammals had relatively high growth hormone levels in comparison to prolactin. Avian and reptilian glands showed lower concentrations of both hormones, with no appreciable differences between them. In amphibians, several species had unusually high prolactin levels and relatively low growth hormone concentrations: growth hormone could not be detected in the salamander (Ambystoma tigrinum). Electrophoretic identification of somatotropins of these tetrapods should permit meaningful studies to be undertaken to elucidate the physiology of this hormone in nonmammalian species.

Blood and pituitary prolactin levels in tilapia (Sarotherodon mossambicus; Teleostei) from different salinities as measured by a homologous radioimmunoassay.

Highly purified prolactin (PRL) of the tilapia (t), Sarotherodon mossambicus, was injected into rats to produce antibodies. A satisfactory antiserum to the tPRL was used to develop a homologous radioimmunoassay (RIA) in which 125I-tPRL was used as the label. The RIA sensitivity (minimal detectable dose) was 0.8 ng of tPRL standard per milliliter. Specificity of the assay was established by demonstrating negligible cross-reactivity of the antiserum with highly purified tilapia growth hormone, a gonadotropin fraction from tilapia pituitaries, and serum from hypophysectomized Sarotherodon. Furthermore, the RIA disclosed that tPRL is highly concentrated in the rostral pars distalis of tilapia kept in either fresh water (FW) or artificial seawater (ASW). The content of immunoreactive tPRL was 6–10 times greater in pituitaries of FW-adapted fish than in glands of those kept in ASW. Serum levels of tPRL were low in fish kept in 100% ASW and they increased 7- to 12-fold with adaptation to FW. Lowering the environmental salinity from 100 to 30% ASW increased the serum level of tPRL only slightly; the major increase in serum PRL concentration in response to hypotonic medium occurs when the environmental salinity is lowered below 10% ASW. Fish adapted to 100% ASW lacking either CaCl2 or MgCl2 did not show elevated serum PRL levels. These results indicated that in tilapia a major stimulus for prolactin secretion is reduced environmental NaCl and/or osmolarity.

Development and preliminary application of a homologous radioimmunoassay for bullfrog prolactin

Abstract A homologous radioimmunoassay (RIA) with high sensitivity was developed for bullfrog prolactin (fPRL). The fPRL used for immunization, iodination, and reference preparation was obtained by disc gel electrophoresis of frog anterior pituitaries. Bullfrog growth hormone (fGH) showed minimal cross-reactivity, and plasma from hypophysectomized frogs had no detectable immunoreactive PRL. The antiserum to fPRL inactivated biologically active PRL in tadpoles and caused accelerated metamorphosis [Clemons, G. K., and Nicoll, C. S. (1977). Gen. Comp. Endocrinol. 31, 495–497.]. The levels of immunoreactive fPRL were determined in individual whole pituitaries and in pooled plasma samples from Rana catesbeiana tadpoles through metamorphic climax (Taylor-Kollros stages XXI–XXV). Pituitary PRL rose slowly from the emergence of the forelegs through stage XXIII and then increased markedly in stage XXIV. Circulating levels paralleled pituitary content, except that the rise during stage XXIV was less pronounced.

PROLACTIN AND THE PITUITARY GLANDS OF FISHES.

Abstract Evidence for the occurrence of prolactin in the hypophysis of fishes is both sparse and unconvincing. In order to re-examine this question, fresh-frozen or acetone-dried pituitary tissues from five teleostean species and three chondrichthyean species were assayed for prolactin content by the pigeon-crop local “micro” method. In addition, assays were performed on media samples obtained from organ cultures of pituitary tissues from five teleostean species and two chondrichthyean species. None of the tissue preparations or media samples elicited responses which were considered typical prolactin reactions, although about 30% of the pigeons injected with these materials showed reactions which were classified as “prolactin-like.” Histological examination of the crops showing these atypical reactions disclosed that the “prolactin-like” reactions were the consequence of intense lymphocytic infiltration of the crop-sac mucosal-submucosal tissues, rather than the typical epithelial proliferation reaction characteristic of the response to injections of mammalian prolactin. Inasmuch as assays of similar preparations from tetrapod pituitaries, including those of amphibians, produced unquestionably typical prolactin responses in the pigeon crop, it seems unlikely that the adenohypophysis of fishes contains a crop sac-stimulating principle.

Effect of mammalian thyrotropin releasing hormone on prolactin secretion by bullfrog adenohypophyses in vitro

The effects of the mammalian thyrotropin-releasing hormone (TRH) on the secretion of prolactin by bullfrog adenohypophysis in vitro were investigated in short-term incubation and 24-hr organ culture experiments. Prolactin in the medium or in the incubated tissue was measured by either polyacrylamide disc gel electrophoresis and densitometry or by a homologous radioimmunoassay. The TRH was consistently effective in promoting prolactin release in vitro in concentrations of 10 ng/ml to 10 μg/ml. The tripeptide also caused an increase in the tissue prolactin content over a wide range of concentrations. These results indicate that TRH may function as a prolactin-releasing factor in the bullfrog.

Effects of antisera to bullfrog prolactin and growth hormone on metamorphosis of Rana catesbeiana tadpoles

Abstract Rabbit antisera to bullfrog prolactin (fPRL) or growth hormone (fGH), or normal rabbit serum (NRS) were injected intraperitoneally into late prometamorphic tadpoles of Rana catesbeiana . The injections were given once a week for 5 weeks at a dose of 50 μl per animal. The fPRL antiserum accelerated metamorphic climax and the GH antiserum did not. The results indicate that endogenous PRL has antimetamorphic effects in this species.

Further analysis of the occurrence of pigeon crop sac-stimulating activity (Prolactin) in the vertebrate adenohypophysis ☆

Abstract Extracts of acetone-dried pituitary glands from representatives of all vertebrate classes were tested for pigeon crop sac-stimulating (PCs) activity using objective, quantitative methods. Extracts of acetone-dried liver and brain tissue combined, or of acetone-dried liver tissue alone, were used to obtain quantitative assessment of nonspecific responses. The crop-sac responses were quantified by removing a standard 4-cm-diameter disc of mucosal epithelium from the site of injection. The dry weight, fat content, and RNA and DNA levels in this disc were determined. Only Tilapia mossambica and Mugil cephalus of eight teleostean species tested gave results which indicated that their “prolactic” had significantly, albeit minimally effective PCs capacity. Responses to other fish pituitaries, including a cyclostome and a chondrichthyean, were not significantly different from those to nonpituitary control tissue. In contrast with the results obtained with the control and fish-pituitary preparations, extracts of the glands of the African lungfish ( Protopterus aethiopicus ), and of anurans, urodeles, and a reptile, were as effectively crop sac-stimulating as extracts of pituitaries from homeotherms. The only species in the lungfish-tetrapod group whose pituitaries did not show more effective PCs activity than all of the fish pituitary preparations was the toad, Bufo marinus . However, the Bufo pituitaries were significantly more effective than the glands of six of the eight teleost species. The possibility that fish pituitaries contain factors which inactivate or interfere with the action of teleost “prolactin” on the crop sac was investigated. An extract of combined pigeon and pollack pituitaries was compared with pigeon pituitary extract alone. The combined extract did not prevent the pigeon prolactin from being fully effective. Extracts of pituitaries from pigeons, lungfish, and three teleostean species were tested for PCs activity at three dose levels. The pigeon and lungfish pituitary extracts gave, in part, log dose-response relationships which paralleled that obtained with ovine prolactin. None of the fish pituitary extracts gave log dose-response relationships which had slopes significantly different from zero. It is concluded that the prolactins of vertebrates in the lungfish-tetrapod line are characterized by a high degree of PCS efficacy. Although the prolactins of some teleostean species may have minimal PCS activity, the pituitaries of fishes characteristically showno specific capacity to stimulate the pigeon crop.

Estimates of parenchymal, stromal, and lymph node deoxyribonucleic acid in mammary glands of C3H/Crg1/2 mice☆☆☆

Abstract The DNA content of intact and mammary gland (MG)-free segments of #4 pads of virgin and lactating C3H/Crg 1 2 female mice was determined. The DNA of inguinal MG lymph nodes was also estimated. The DNA of the MG-free-pad did not change between the virgin and lactational states; MG-DNA in the intact virgin and lactating fat pads was 23% and 89% of the total DNA, respectively. In lactating mice, MG-DNA increased 27-fold over that present in virgin mice. Inguinal lymph node DNA was 8.5 times greater than the MG-DNA of virgins and about 31% as high as the MG-DNA of the lactating gland.