Effect of diverse mammalian and nonmammalian gonadotropins on isolated rat Leydig cells

Dose and time relationships of intravenously injected rat recombinant luteinizing hormone and testicular testosterone secretion in the male Rat

The ability of hCG and LH to induce testosterone (T) secretion by Leydig cells is well documented. However, the influence of the pulsatile nature of LH secretion, with varying frequency and amplitude, on T production in vivo is less clear. In our earlier studies on the relationship between pulsatile LH release and T secretion in adult male rats, no simple causality was observed. The recent availability of rat recombinant (rec) LH prompted us to study the effects of one and of three i.v. pulses of different doses of rat recLH on T secretion in adult male rats rendered hypogonadotropic by treatment with the GnRH antagonist cetrorelix. One or three supraphysiological pulses of 1.0 microg of rat recLH produced similar maximal T responses. In contrast, high physiological LH pulses (0.1 microg) produced discrete T-response peaks, whereas multiple low pulses of LH (0.03 microg) were needed before a T response was achieved. The T stimulation was greatly diminished after an LH pulse of 0.1 microg if rats had been treated on the previous day with pulses of 0.03 vs. 0.1 microg rat recLH, apparently because of prolonged LH deprivation and lack of Leydig cell priming due to the GnRH antagonist treatment. The novel preparation of rat recLH provides a physiologically relevant tool for studying the complex relationship between pulsatile LH release and T secretion in male rats.

Effects of diverse mammalian and nonmammalian gonadotropins in a rat granulosa cell bioassay for follicle-stimulating hormone

The biopotencies of pituitary gonadotropins purified from a marsupial (kangaroo), two avian (ostrich and turkey), a reptile (turtle), an amphibian (bullfrog), and two fish (sturgeon and teleost) species were examined using an in vitro rat granulosa cell bioassay for follicle-stimulating hormone (FSH). Treatment of cultured granulosa cells with increasing concentrations of gonadotropin preparations from these species resulted in dose-dependent increases in estrogen production from negligible amounts to maximal levels of approximately 2-29 ng/culture. The relative biopotencies of these FSH preparations from most potent to least potent were in the order of human greater than ostrich greater than turkey greater than kangaroo greater than turtle greater than sturgeon greater than bullfrog greater than teleost with ED50 values of human 8.7 ng/well; ostrich 10.5 ng/well; turkey 22.5 ng/well; kangaroo 58.2 ng/well; turtle 62.5 ng/well; sturgeon 260 ng/well; bullfrog 750 ng/well; teleost greater than 1000 ng/well. In contrast, luteinizing hormone (LH) preparations were considerably less effective for ostrich, turkey, kangaroo, turtle, and bullfrog, being six-, five-, three-, and twofold less potent than FSH preparations for the same species, demonstrating the specificity of this assay for FSH. An LH preparation from bullfrog was unable to significantly stimulate estrogen production below 500 ng/ml. Thus, the present in vitro bioassay (GAB) using rat granulosa cells provides a sensitive and specific assay for measuring FSH activities of gonadotropins from diverse mammalian and nonmammalian species.

Gonadotropin action on androgen synthesis in short-term incubation of explants and dispersed cells of the testis of Xenopus laevis

Testis cells of the toad Xenopus laevis were dissociated with collagenase and the cell suspension was enriched for steroidogenic cells by Percoll gradients. Results suggested that cells should be preincubated during a 6-h period before stimulation with gonadotropin. Our results indicate that a 2-h incubation period with gonadotropin was necessary to obtain a significant response. Furthermore, the cells can be maintained in a functional state longer than mammalian testis cells. Different gonadotropins were used to stimulate androgen production, and their effects were compared in both dissociated cells and testicular explants. Cells were more sensitive to luteinizing hormone (LH) and follicle stimulating hormone (FSH) than the explants (ED50LH = 0.041 +/- 0.003 micrograms for cells and 0.097 +/- 0.002 micrograms for explants: ED50FSH = 0.41 +/- 0.03 micrograms for cells and 0.63 +/- 0.03 micrograms for explants). Moreover, human chorionic gonadotropin (hCG) which only stimulates testicular explants at high doses, failed to stimulate the androgen production of dissociated cells; this indicates a low sensitivity of amphibian testis to hCG and a possible damaging effect of collagenase on the receptors of isolated cells.

Characterization of a monoclonal antibody which detects luteinizing hormone from diverse mammalian species

The present study describes the development and characterization of a monoclonal antibody (518B7) generated against bovine LH (bLH). Although 518B7 was extremely specific for LH, very low species specificity was observed. A RIA using this antibody and radioiodinated equine LH (eLH) showed good sensitivity for all mammalian LH preparations tested, with the exception of human LH (15%, relative to the eLH reference standard). Activities of most mammalian LH's ranged between approximately 50-200%. Much less activity was detected with reptilian LH (less than 1.5%). Amphibian and avian LH fractions were essentially inactive. The reactivities of LH alpha and beta subunits from a variety of mammals clearly showed that the antibody reacts with the beta subunit. Sensitive RIAs were also developed utilizing 125I-bovine and 125I-rat LH. Interestingly, all hormone preparations which showed sufficient reactivity for statistical analysis within the dose ranges used in the present study (0.01-1000 ng/tube) produced a displacement curve parallel to the reference standard. We have also validated the use of 518B7 in detecting LH in serum. Parallel dilution curves relative to purified LH reference standards were observed with equine and bovine serum samples and equine pituitary extract. High (average 94%) recoveries were also seen with bovine serum with known amounts of exogenously added bLH. Similar patterns of LH secretion were detected with a RIA based upon 125I-bLH and 518B7 and a previously described polyclonal antibody-based RIA in bovine serum samples during estrus. Thus, a monoclonal antibody for LH has been produced which can be used to develop sensitive and specific RIAs in many different mammalian species.(ABSTRACT TRUNCATED AT 250 WORDS)

Species variation of gonadotropic activity in an in vitro assay measuring androgen formation by carp (Cyprinus carpio) testis with special reference to bioassay of piscine gonadotropins

The objectives of this study were to establish a suitable and validated in vitro bioassay of piscine gonadotropins (GTHs) by using a carp testis androgen production system and to compare the androgenic responses in such an assay to gonadotropins from various vertebrate species. The testes from mature carp with gonadosomatic indices of 8-30% were used. Androgen production was first compared with respect to methods for preparation of the carp testis (sliced, minced, homogenized, and collagenase-dispersed testis preparations). The time course of androgen formation, the effects of xanthine and theophylline, and other factors on androgen production also were investigated. Theophylline was more effective than xanthine in potentiation of gonadotropin-evoked androgen formation by carp testis. The testis preparations were incubated in medium 199 (pH 7.40) containing 2 mM theophylline with shaking at 100 cycles/min at 25 degrees C for 4 hr. Homogenized testis preparations had limited ability for androgen production, while sliced, minced, and minced-collagenase-dispersed testis preparations were highly responsive to gonadotropins for androgen production. The minced testis preparation, utilizing 100 mg/ml incubation medium per vial, was chosen as the standard incubation procedure in this study. The minced testis androgen production assay was highly sensitive to gonadotropins from several piscine species (silver carp, common carp, and salmon), and all these GTHs produced parallel dose-related androgen production curves. Mammalian GTHs were also capable of promoting androgen formation by carp testis, but they were much less potent than were piscine GTHs. Pregnant mares' serum gonadotropin (PMSG) was more effective than human chorionic gonadotropin (hCG) in evoking carp testis androgen production.(ABSTRACT TRUNCATED AT 250 WORDS)

A factor from bursa of Fabricius inhibits in vitro the chorionic gonadotropin response of the chick testis

The effect of bursa of Fabricius on the endocrine function of the chick testis was studied using an isolated testis cell preparation. Testosterone secretion, both basal and under hCG stimulation, was measured in the incubation medium. The bursal extract inhibited the response of the testis cells to hCG detected as a reduced testosterone secretion. The normal basal secretion of the testis cells was not modified by the bursal extract. To analyze some characteristics of the bursal factor, fractions of approximately known molecular weight were obtained by filtering through Amicon membranes. The active factor was found in the fraction corresponding to 1000-10000 Da. Its activity disappeared after heating of trypsin incubation, suggesting the peptidic nature of the bursal factor. Tissue extracts from gut and spleen did not modify the hCG response of the testis cells. There was inhibition of the hCG response by thymus extracts of the newly hatched chicken. These results add new evidence of a modulatory effect of the immunogenic organs on the endocrine function of the testis in the newly hatched chicken.

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.

The dynamics of the steroidogenic response of perfused Xenopus testis explants to gonadotropins

The dynamics of androgen production by perfused Xenopus testis explants has been investigated under various gonadotropic stimulations. Androgens were measured in perfusate by radioimmunoassay. The behavior of hormones in the perfusion system was assessed. Pieces of testis were capable of producing androgens after more than 20 hr in perifusion. Amplitude and duration of the response to a gonadotropic stimulation were the same 3 and 10 hr after the beginning of the experiment. After stimulation by pituitary extract, hCG, or carp GTH, there was a rapid tenfold increase in androgen secretion with a maximum after 1.5 hr and then a slow decrease to a basal line level. A typical log dose-response curve was obtained with hCG and cGTH. After 6 hr continuous stimulation by pituitary extract, steroid secretion increased and reached a plateau 4 hr later. The decrease occurred only after the end of stimulation. The same amount of pituitary extract injected into the column at the rate of 4 min stimulations every hr gave the same type of response. As far as is known, the present data are the first on perifusion systems on the testes of lower vertebrates.

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.

Variations in the properties of equine chorionic gonadotropin

The objectives of this paper are to review the chemical and biological properties of equine chorionic gonadotropin (eCG, PMSG) isolated from the serum. Comparisons are made with eCG isolated from endometrial cups, trophoblast cell culture medium, and low titer serum. The results show that eCG can vary, depending on the source, in both chemical and biological (LH and FSH activity) properties.

Rabbit lutropin: preparation, characterization of the hormone, its subunits and radioimmunoassay

The purification of rabbit lutropin is described. A product with a potency of 1.53 X NIH-LH-Sl was obtained as assayed by the ovarian ascorbic acid depletion assay. In a homologous radioimmunoassay, which is described, rabbit lutropin has a potency 4.83 X NIH-LH-Sl. In a radioligand assay, utilizing labeled ovine lutropin as the trace, the relative potency was 0.47 X NIH-LH-Sl measured by 50% inhibition comparison since rabbit lutropin response in this system did not parallel ovine lutropin. A counter-current distribution procedure for separation of rabbit lutropin subunits is described. Amino acid composition of the isolated subunits and intact rabbit lutropin was determined. The carbohydrate composition of the latter is presented; only amino sugar determinations are available for the subunits. The NH2-terminal amino acids are phenylalanine (alpha subunit) and alanine (beta subunit). Preliminary data on COOH-terminal amino acids are provided.