Search PubMed⌕ Search

Biomedical subjects

P Licht

Publications and source records attributed to P Licht.

At least 127 records · Page 7Linked to original sources
PubMed1984

Effects of chicken and mammalian gonadotropin-releasing hormones (GnRH) on in vivo pituitary gonadotropin release in amphibians and reptiles.

The ability of mammalian and chicken gonadotropin-releasing hormones (GnRH) and their agonistic analogs to stimulate in vivo gonadotropin release were tested in a frog (Rana catesbeiana), snake (Naja naja), and turtle (Sternotherus odoratus). In the frog, chicken and mammalian GnRH were equipotent in stimulating the release of FSH and LH. Attendant increases in plasma androgen and the occurrence of spermiation confirmed the release of biologically active gonadotropin. Neither of the GnRH preparations or their agonists produced significant changes in plasma hormones in either of the reptiles. In light of comparable data for the actions of these GnRH preparations in mammals and birds, it appears that species specificity in the response to different GnRHs does not correlate well with the nature of the homologous hypothalamic GnRH molecule.

Animals↗
PubMed1984

Presence of a neurophysin-like precursor in the green turtle (Chelonia mydas).

A glycoprotein of neurohypophysial origin was found to have cofractionated with FSH prepared from pituitary glands of the green turtle, Chelonia mydas. Antiserum raised against this preparation contained high antibody titres and affinity for the neurohypophysial component and allowed development of a specific radioimmunoassay to monitor its purification and distribution in the brain. Immunocytochemistry revealed that the glycoprotein was concentrated in the pars nervosa and associated nerve tracts passing through the median eminence to the supraoptic and paraventricular nuclei; similar distributions were observed in turtles and rats. The antiserum to the turtle material bound radiolabelled rat vasopressin (VP)-neurophysin and precipitated precursors of this neurophysin, but it did not cross-react with rat oxytocin-neurophysin. An amino-terminal alanine was also consistent with the structure of rat VP-neurophysin, but the turtle molecule was larger than the corresponding rat molecule. Limited tryptic digests of the turtle glycoprotein contained two components, one of which bound to lysine VP. Both components contained carbohydrate, but only the one which bound to VP cross-reacted in a radioimmunoassay for rat VP-neurophysin. The apparent surge in plasma immuno-FSH at the time of oviposition previously described in the turtle probably represented release of a neurophysin-like 'carrier' molecule associated with secretion of the neurohypophysial hormone (e.g. arginine vasotocin; AVT) responsible for oviduct contractility. These data suggest that the neurohypophysial glycoprotein represents a partially processed AVT precursor and provide the first biochemical evidence of a mammalian-like biosynthetic pathway for neurohypophysial hormones in a non-mammalian species.

Amino Acids↗
PubMed1983

Subunits of an avian (ostrich) follicle-stimulating hormone and their hybridization with subunits of mammalian gonadotropins.

Follicle-stimulating hormone (FSH) from the ostrich, Struthio camelus, was dissociated by methods previously used to prepare subunits from mammalian gonadotropins. Two chemically dissimilar subunits were obtained from the ostrich FSH and these resembled the alpha- and beta-subunits of mammalian FSH in amino acid composition. The subunits were relatively inactive in radioimmunoassay, radioreceptorassay, and bioassay when tested alone, but significant activity was regenerated upon their recombination. Incubations of mixtures of one of the ostrich subunits with the opposing subunit of ovine FSH also resulted in a significant regeneration of binding and biological activity in FSH assays. These hybrid recombinants demonstrated that the species specificity of the FSH molecule is conferred entirely by the source of the beta-subunit; in fact, hybrids formed between ovine LH-alpha and either ovine or ostrich FSH-beta were more potent in FSH assays than were those containing even two homologous FSH subunits. In contrast, there was little regeneration of LH bioactivity when FSH subunits (from ostrich or sheep) were combined with the subunits of ovine LH, although some LH binding activity was obtained when the mixture contained either one of the LH subunits; i.e., even LH-alpha + FSH-beta showed significant enhancement of binding activity for LH receptors. Thus, the subunits of avian FSH show biochemical and functional homologies to those of mammalian FSH, but there is only limited interchangeability with ovine LH subunits.

Amino Acids↗
PubMed1983

Specificity to gonadotropins in the response of in vitro estrogen secretion by fish ovaries.

Gonadotropin preparations from three classes of tetrapods (amphibian, avian, and mammalian) and a chondrosteian and teleost fish were used to investigate the species specificity and hormonal (FSH/LH) specificity of in vitro steroid (estradiol-17 beta) production by the teleost ovary. Results for ovaries from one species of gobiid, Gillichthys mirabilis, and two cichlids, Cichlasoma citrinellum and Sarotherodon mossambicus, revealed a general lack of species specificity in the response to tetrapod gonadotropins, but the piscine, especially sturgeon, gonadotropins were much more potent than any of the tetrapod hormones. All three species of teleost ovaries responded to both types of tetrapod gonadotropins (FSH and LH), but the extent of hormonal specificity was variable. The gobiid ovary showed the highest LH specificity (potencies of FSHs = 7-14% of LH); in the two cichlids the potency of FSHs ranged from 11 to 100% of the respective LHs. In general, the specificity of the ovarian steroidogenic response to gonadotropins parallels that observed for testosterone secretion in the males of the same three fish, but the differential actions of the tetrapod hormones (both species and hormonal specificity) are more exaggerated for the testes.

Animals↗
PubMed1983

Biological and binding activities of pituitary hormones from the ostrich, Struthio camelus.

Biological and binding activities of adenohypophysial hormones purified from the ostrich (ost), Struthio camelus, were compared to those of the corresponding hormones derived from mammalian and other avian species. The potency of ostrich prolactin was comparable to those of other avian preparations and slightly less active than the ovine hormone when tested in the pigeon crop-sac assay, but ostrich growth hormone (GH) was more potent than several other avian preparations and was comparable to mammalian GH in the rat tibia bioassays. Marked discrepancies were evident in the activities of both ostrich gonadotropins (ostGn) when they were tested in a variety of in vivo and in vitro bioassays and radioreceptor assays (RRAs). Both the ostrich follicle-stimulating hormone (ostFSH) and luteinizing hormone (ostLH) were among the most potent tested thus far in in vivo bioassays for total gonadotropin in a lizard and a cockerel; a high sialic acid content may account for these high potencies. OstFSH was also the most potent nonmammalian Gn tested in two FSH specific mammalian bioassays, an in vivo (ovarian augmentation) and an in vitro (cAMP production) rat bioassay; in fact, ostFSH behaved more like a mammalian than an avian hormone in these assays. However, the binding activity of ostFSH was not unlike that of other avian FSH preparations when tested in either mammalian or nonmammalian FSH-RRA systems. OstLH was more potent than other avian preparations in an in vitro mammalian bioassay, but not in avian or amphibian LH bioassays; species specificity was pronounced among these LH assays. Binding activities of ostLH in mammalian and avian LH-RRAs were generally consistent with potencies in the two species of bioassays. However, a marked discrepancy was apparent in the behavior of ostLH in FSH-RRAs. Although ostLH had very low FSH activity when tested by radioimmunoassay, by bioassay, or by FSH-RRA with avian gonads, it was equipotent to ostFSH in competing for FSH-binding sites on the mammalian gonad; in this respect it was more like turkey than chicken LH. The ability of ostLH to antagonize the biological activities of ostFSH in the stimulation of cAMP by rat seminiferous tubules confirms that ostLH binds to the same functional receptors as FSH on the rat testis, even though it does not induce the characteristic physiological response associated with FSH.

Animals↗
PubMed1983

Relation between acute pituitary responsiveness to gonadotropin releasing hormone (GnRH) and the ovarian cycle in the bullfrog, Rana catesbeiana.

Freshly captured female bullfrogs (Rana catesbeiana) were challenged with a standard dose (2 micrograms) of gonadotropin-releasing hormone (GnRH) shortly before and at the onset of the spawning season (in early April and mid-May) to examine the relationship between pituitary responsiveness and ovarian stage; males were also tested in April. As shown previously, increments in plasma gonadotropins induced by GnRH were consistently lower in females than in males. There was little difference in average responsiveness between the two collections of females and results for these were similar to those obtained at other times of the year. A wide range of ovarian stages was represented at both collection times as evidence by plasma steroid profiles, but there was no correlation between the GnRH-induced increments in plasma FSH and LH and plasma levels of androgens (testosterone and 5 alpha-dihydrotestosterone), estradiol-17 beta, or progesterone in the 71 females tested. Thus, there is no evidence of a feedback effect of ovarian steroids on the pituitary responsiveness to acute GnRH stimulation in the frog as has been demonstrated in mammals.

Animals↗
PubMed1983

Seasonal and stress related changes in plasma gonadotropins, sex steroids, and corticosterone in the bullfrog, Rana catesbeiana.

Studies of seasonal gonadal cycles combined with direct measurements of plasma levels of the two gonadotropins (FSH and LH), several gonadal steroids (estrogen, E; progesterone, P; testosterone, T; and 5 alpha-dihydrotestosterone, DHT), and the interrenal steroid corticosterone (B) were made in male and female bullfrogs in central California over a 5-year period (between 1976 and 1981). During the course of these studies, we discovered that levels of plasma gonadotropins and steroids are highly labile and particularly sensitive to the effects of captivity, especially in males. In animals captured and sampled repeatedly in the field over a 3-day period, hormone levels remained constant, but if held in collecting sacks, gonadotropin and gonadal steroids began to drop within 2--4 hr and usually reached "baseline" levels within 20 hr. This effect was apparent in all seasons, except occasionally in early spring when hormone levels dropped by only about half. Hormone levels were also generally depressed by the time commercially collected frogs reached local supply houses. Plasma B increased within 30 min of capture and remained high for days in captive animals. Blood samples taken from several hundred animals at the time of capture reveal pronounced seasonal cycles in all hormones measured. These changes are discussed in connection with other gross changes in gonadal condition and with regard to possible interactions among gonadotropins and steroids. Both sexes show a general elevation of hormone levels in spring and early summer, but the sexes differ somewhat both in timing and in magnitude of the changes, as well as in the nature of the dominant steroids. Pronounced "surges" in gonadotropins are evident around the time of gamate release in bot sexes, but the temporal pattern of these surges is not the same for ovulation and spermiation; an elevation in plasma P is associated with the periovulatory surge in gonadotropins. Results were not entirely consistent with expectation of pituitary--gonadal relationships. Levels of plasma gonadotropins and steroids did not show the reciprocal relationship expected from a simple negative feed-back between gonadal and pituitary secretion, nor did changes in gonadotropins and gonadal activities show the consistent positive correlation expected from a direct dependence of gonadal function on circulating gonadotropins. In females, plasma T, but not E, correlated with ovarian growth. Plasma T in females reached much higher levels than in males, but DHT was higher in males. Androgens were generally elevated during the period of sexual activity in males, but absolute levels did not correlate well with individual differences in sexual behavior. Thus, seasonal changes in testicular and ovarian activities cannot be accounted for solely by seasonal cycles in circulating gonadotropin levels.

Androgens↗
PubMed1983

Circannual and seasonal variations in plasma luteinizing hormone levels of ovariectomized ground squirrels (Spermophilus lateralis).

Plasma luteinizing hormone (LH) levels were determined at monthly intervals in intact and ovariectomized squirrels maintained in a constant 14L:10D photoperiod at a temperature of 23 +/- 2 degrees C. LH was undetectable (less than 0.9 ng/ml) in plasma of intact females at all times of year. Females ovariectomized (OVX) at 9.5 months of age in March showed substantial increases in plasma LH in May and June but LH was undetectable between July and November. Females ovariectomized at 13 months of age in July first manifested detectable LH levels the following January and February (6-7 months post-ovariectomy). Very few adult females trapped in May and ovariectomized in August had detectable LH levels within 2 months of ovariectomy; however, females ovariectomized the following February had detectable LH titers 1 month later. Long-term studies of individual OVX squirrels indicated peak LH levels between March and June, 1980, relatively low or undetectable titers between August and December and elevated LH levels between January and March, 1981. The results are suggestive of a circannual rhythm of LH secretion which appears restricted to one season of the year and occurs independently of steroid feedback from the ovaries; ovarian steroids only modulate the levels of plasma LH during the brief annual period of hypothalamo-hypophysial activity. We suggest that onset and termination of LH release are mediated by central nervous system circannual clocks.

Animals↗
PubMed1983

Seasonal variations in plasma luteinizing hormone levels of gonadectomized male ground squirrels (Spermophilus lateralis).

Plasma luteinizing hormone (LH) levels were determined at monthly intervals in intact and orchidectomized ground squirrels maintained in a constant 14L:10D photoperiod at a temperature of 23 +/- 2 degrees C. Animals were orchidectomized or sham operated at different ages and at different stages of the annual reproductive cycle. LH levels were elevated in orchidectomized as compared to intact males within 1 month, and often within 48 h, after orchidectomies performed either before or after the normal breeding season. LH levels tended to remain chronically elevated in long-term orchidectomized males. Although negative feedback regulation of LH by the testes was evident at most stages of the reproductive cycle, effects of orchidectomy on LH were most pronounced during the nonbreeding season when plasma LH titers of intact males were at their annual nadirs, and less pronounced or absent during the breeding season when levels were normally elevated in intact males. For most of the year male gonadal hormones exert negative feedback on LH release. We hypothesize that under the influence of a circannual timing mechanism, sensitivity to steroid feedback is reduced as the breeding season approaches and LH secretion increases despite the attendant rise in plasma androgen levels. These results contrast with data for female squirrels in which there is a seasonally restricted and characteristically brief elevation of plasma LH after ovariectomy; in females, but not in males, onset and termination of LH secretion appear to be regulated by a circannual clock that functions independently of gonadal secretions.

Animals↗
PubMed1983

Effects of gonadectomy on polymorphism in stored and circulating gonadotropins in the bullfrog, Rana catesbeiana. I. Clearance profiles.

Marked differences were observed between the clearance profiles of immunoreactive plasma gonadotropins in gonadectomized and intact male bullfrogs (Rana catesbeiana). The disappearance patterns of endogenously secreted follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from plasma of intact animals following chronic (1-4 days) infusion with gonadotropin releasing hormone (GnRH) showed multiple components, but the initial few half-lives were relatively short (less than 1 h) and about 90% of both gonadotropins were cleared from the plasma within 6 h. Hypophysectomy had no effect on gonadotropin clearance rates following the termination of GnRH infusion. Clearance profiles of exogenous gonadotropins after chronic (6 h) infusion of bullfrog pituitary extract were similar to those observed after GnRH infusion. Gonadectomized frogs also cleared these infused pituitary gonadotropins at the same rate as intact animals, confirming that gonadectomy did not impair peripheral clearance mechanisms. Relatively rapid clearance rates were also observed for endogenous FSH and LH in normal untreated frogs. By comparison, the disappearance rates of FSH and LH from plasma of six long-term gonadectomized males following hypophysectomy were extremely slow: first half-lives for FSH and LH were 25.6 h and 17.2 h, respectively, and subsequent half-lives were even longer. Several weeks were required to clear fully the FSH and LH from the circulation in these males. Thus, a significant change in the physicochemical form of the circulating gonadotropins after gonadectomy in the male bullfrog is postulated; the corresponding changes in clearance rates were considerably greater than have been observed in any other species.

Animals↗
PubMed1983

Effects of gonadectomy on polymorphism in stored and circulating gonadotropins in the bullfrog, Rana catesbeiana. II. Gel filtration chromatography.

Marked polymorphism was revealed in both stored and circulating forms of immunoreactive follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in the bullfrog, Rana catesbeiana, by exclusion chromatography on columns of Sephracyrl-S200. FSH behaved as a more homogeneous and larger molecule than LH from the same pituitary or plasma, but the properties of both hormones in the plasma were markedly affected by gonadectomy. Chromatographic profiles of FSH stored in the pituitaries were similar in intact and gonadectomized frogs, but pituitary LH in the latter was comprised of a larger proportion of early eluting activity. Previously purified preparations of bullfrog FSH and LH were more homogeneous than these extracts. Differences between pituitary hormones in intact and gonadectomized frogs were small compared with those between circulating hormones. Plasma FSH and lH from gonadectomized frogs behaved as more homogeneous and larger molecules than those from intact frogs in which plasma gonadotropins were elevated normally or by injections with gonadotropin releasing hormone (GnRH). Some differences in circulating hormones were also observed between a normal male and female and both differed from gonadectomized an GnRH-treated intact frogs. Chromatographs of plasma gonadotropins in GnRH-treated animals generally resembled those of the hormones stored in the pituitary, whereas plasma FSH and LH in gonadectomized frogs appeared more homogeneous and larger than the pituitary-stored forms. Those pronounced differences in chromatographic properties of gonadotropins in intact and gonadectomized frogs correlate with previously observed effects of gonadectomy on clearance profiles of circulating FSH and LH.

Animals↗
PubMed1983

Induced ovulation and changes in pituitary responsiveness to continuous infusion of gonadotropin-releasing hormone during the ovarian cycle in the bullfrog, Rana catesbeiana.

Chronic (2-4 days) constant-rate infusions of mammalian gonadotropin releasing hormone (GnRH) were performed in female bullfrogs, Rana catesbeiana. The magnitude and temporal relationship of profiles of plasma follicle-stimulating hormone (FSH), luteinizing hormone (LH) and sex steroids [testosterone (T), estradiol-17 beta (E2) and progesterone (P)] during GnRH infusion were dependent on ovarian stage. However, in all females, the same biphasic increase in plasma gonadotropins was apparent and initial elevations in gonadotropins were accompanied by correlated increments in plasma T and E2. Complete pituitary "desensitization" to chronic GnRH infusion was not observed. Females in early follicular stages were relatively unresponsive to infusions of 1.0-10.0 micrograms/h GnRH; elevations in plasma LH were marginal and FSH was unchanged. Females with fully developed (preovulatory) ovaries were more responsive: infusion of 1.0 micrograms/h GnRH produced significant elevations in plasma LH by 2 h followed by even larger increases ("surges") after 12 h. This LH "surge" was preceded by a decline in plasma T and E2 and was accompanied by abrupt elevations in plasma P and by ovulation. Postovulatory females showed a more gradual and smaller increase in plasma LH. Infusion of GnRH in the female bullfrog establishes a clear relationship between pituitary responsiveness and the ovarian cycle not evident from acute GnRH injection; GnRH was most effective immediately before ovulation. These data are also the first to detail periovulatory changes in plasma gonadotropins and ovarian steroids in an amphibian.

Animals↗
PubMed1982

Morphology and immunocytochemistry of the turtle pituitary gland with special reference to the pars tuberalis.

Examination of pituitaries from young and adult turtles representing four families, reveals that in addition to the abundant juxtaneural pars tuberalis (juxPT) found in this class of reptiles, there is generally a substantial amount of pars tuberalis (PT) tissue closely associated with the pars distalis (PD). The PT forms a cortical layer especially conspicuous around the anterior tip of the PD in some species (Trionyx, Kinosternon, Sternotherus), or it forms a thick dorsal layer of tissue irregularly extending onto the sides of the PD in others (Pseudemys, Chrysemys, Lepidochelys, Chelonia). Immunocytochemical studies using unlabelled second antibody and peroxidase-antiperoxidase reveal that in turtles of all ages, the PT tissue allied with the PD (the PTinterna) is composed primarily of cells containing glycoprotein hormones (FSH, LH and TSH), especially the gonadotropins. The juxPT, however, consists mainly of secretory cells unstained by the antisera tested and includes only a small number of gonadotropes and thyrotropes. Although usually widely distributed in the testudinate adenohypophysis, the great majority of gonadotropes and thyrotropes present in the hatchling are in the PTinterna. It is probable that a concentration of these cells in the PTinterna is widespread among vertebrates. In all turtles examined, lactotropes occur principally in the anterior and ventral part of the PD proper; somatotropes are posterior and dorsal. Corticotropes are concentrated as the lactotropes in the anterior PD, but some are also scattered throughout the posterior half of the gland. Lactotropes, corticotropes, and with a few exceptions, somatotropes, do not occur in PT tissue in the turtle.

Adrenocorticotropic Hormone↗
PubMed1982

Circannual rhythms of plasma testosterone and luteinizing hormone levels in golden-mantled ground squirrels (Spermophilus lateralis).

Male squirrels, born approximately June 1 and kept under constant conditions of photoperiod (14 h of light per day) and temperature (23 +/- 2 degrees C) from birth, manifested circannual rhythms in plasma testosterone (T) and luteinizing hormone (LH) levels. Blood samples were collected once per month for 22 months and hormone levels determined by radioimmunoassay. Testosterone levels were low or undetectable ( less than or equal to 0.05 ng/ml) between October and January of the first year, and began increasing in February and peaked during April and May (approx. 4.5 ng/ml). By August of the second year T had declined to low levels which were maintained through January (0.05 ng/ml). The cycle then repeated, with T titers elevated during April and May of the second year. LH levels were undetectable (less than or equal to ng/ml) throughout most of the first 8 months of life; LH peaks were reached by individual animals between March and July. There was a close correspondence between seasonal peaks and troughs of testosterone and those in LH. The circannual pattern of plasma T and LH also was documented for a group of field-trapped males (less than or equal to 11 months old) maintained under similar conditions and bled at monthly intervals for 14 consecutive months. Rhythms of plasma T and LH persisted with a period of 11 to 12 months under constant conditions and thus qualify as circannual cycles.

Aging↗