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Biomedical subjects

R E Peter

Publications and source records attributed to R E Peter.

At least 145 records · Page 8Linked to original sources
PubMed1988

Effect of teleost GnRH on reinitiation of oocyte meiosis in goldfish, in vitro.

The effects of native and an agonist analogue of teleost gonadotropin-releasing hormone (GnRH) [(D-Arg6, Trp7, Leu8, Pro9-NHEt)-GnRH; tGnRH-A] on the hormone-induced meiotic maturation of goldfish oocytes were investigated. Incubation of follicle-enclosed goldfish oocytes with either carp gonadotropin (GtH) or meiogenic progestogens, including 17 alpha-hydroxyprogesterone (HP) and 17 alpha,20 beta-dihydroxyprogesterone (DHP), reinitiated oocyte meiosis in vitro, as indicated by germinal vesicle dissolution (GVD). Addition of tGnRH-A (10(-7) M) significantly attenuated the GVD response to GtH, HP, and DHP in a dose-related fashion; tGnRH-A reduced the magnitude of progestogen-induced GVD response without significantly affecting the sensitivity of the oocytes to the meiogenic steroids. Similarly, administration of native teleost GnRH (tGnRH) significantly attenuated GtH-induced GVD response, although the 50% maximal response of the native peptide was significantly higher than that of tGnRH-A (380.9 +/- 125 and 2.72 +/- 0.94 nM, respectively). The present results provide the first demonstration of an inhibitory action of a GnRH agonist on the process of progestogen-induced oocyte meiosis and support the hypothesis that GnRH or a GnRH-like peptide might play a modulating role in the control of oocyte meiosis at the ovarian level in goldfish.

Animals↗
PubMed1987

Gonadotropin production and release in female goldfish (Carassius auratus) after administration of pimozide and an LHRH analogue as studied by electron microscopy and radioimmunoassay.

The effect of pimozide and an LHRH-analogue (LHRH-A) on gonadotropic cells of the goldfish pituitary gland were described qualitatively and quantitatively. A scale of four categories was devised to reflect various ultrastructural appearances of the cells. Experimental animals were divided into a control group, a group injected with LHRH-A alone, pimozide alone, and groups receiving these two substances in combination. Fish injected with the single substance were killed 12 h after injection while the groups receiving the combined treatments were killed at 4, 12 and 48 h. Serum levels of gonadotropin measured by radioimmunoassay were used to indicate whether an increase in hormone release had occurred. An immunocytochemical technique, the protein A-gold procedure, assured that the cells studied were gonadotropes. The control group showed variation in the profiles of gonadotropic cells. The single treatment groups showed some increase in secretory inclusions. At 4 h after injection the combined treatment caused a significant increase in hormone granules; at 12 and 48 h there was a gradual decrease in content of secretory products, and an increase in vacuolization. The results indicate that the combined pimozide and LHRH-A treatment stimulated gonadotropin production as well as release.

Animals↗
PubMed1987

Activity of position-8-substituted analogs of mammalian gonadotropin-releasing hormone (mGnRH) and chicken and lamprey gonadotropin-releasing hormones in goldfish.

Several vertebrate gonadotropin-releasing hormones (GnRH) and analogs were tested for activity in vivo in goldfish. Each peptide was administered intraperitoneally to goldfish, pretreated with pimozide or vehicle for pimozide, and changes in serum levels of gonadotropin were determined. Pimozide potentiates the activity of GnRH in vivo in goldfish by blocking the endogenous gonadotropin release-inhibitory activity of dopamine; relative potencies of GnRH peptides become evident in vivo in goldfish pretreated with pimozide (R. Peter et al. (1985), Gen. Comp. Endocrinol. 58, 231-242). Mammalian GnRH (mGnRH) was used as reference standard. [Try3, Leu5, Glu6, Trp7, Lys8]-GnRH (lamprey GnRH), [Gln8]-GnRH (chicken GnRH-I), and [His5, Trp7, Try8]-GnRH (chicken GnRH-II) caused increases in serum gonadotropin level similar in magnitude to mGnRH. [His5, D-Arg6, Trp7, Tyr8]-GnRH is superactive in the goldfish. [Asn8]-, [Met8]-, [Phe8]-, and [Ser8]-GnRH had activity similar to mGnRH in goldfish; [His8]-, [Ile8]-, and [Leu8]-GnRH had a lower level of activity; [Glu8]-GnRH had no apparent activity. The results indicate that there is no particular requirement for a hydrophobic or hydrophilic amino acid, or for a positively charged amino acid in position 8 of mGnRH for activity in vivo in the goldfish; a negatively charged amino acid in position 8 is detrimental for activity.

Animals↗
PubMed1987

Increased gonadotropin levels in goldfish do not result in alterations in circulating thyroid hormone levels.

To determine whether increases in gonadotropin levels are capable of altering thyroid function in goldfish, plasma thyroid hormone levels were measured following induced changes in endogenous gonadotropin secretion and injection of carp gonadotropin. Radio-frequency lesions placed in the nucleus preopticus periventricularis or monosodium-L-glutamate-induced lesions of the posterior nucleus lateralis tuberis (NLT) of the hypothalamus were capable of stimulating significant increases in plasma gonadotropin levels, but were without effect on plasma triiodothyronine (T3) or thyroxine (T4) at time intervals ranging from 5 hr to 10 days. Likewise, injections of a superactive analog of gonadotropin-releasing hormone resulted in profound increases in gonadotropin levels without associated changes in thyroid hormones. No changes in the circulating levels of T4 or T3 were observed in response to injection of purified carp gonadotropins whereas injection of bovine thyrotropin or carp pituitary extracts stimulated significant increases in T4. Radiofrequency lesions of the pituitary stalk or of the anterior NLT also resulted in significant increases in circulating levels of T4, but not of T3, at 10 and 30 hr postlesion. These results demonstrate that direct acute stimulation of circulating thyroid hormone levels is not an intrinsic action of endogenous goldfish gonadotropin and that activation of the reproductive system, leading to ovulation in some cases, is without effect on blood total thyroid hormone levels. Additionally, these results confirm that hypothalamic inhibition of the pituitary-thyroid axis exists in this teleost fish and demonstrate that interruption of this inhibition results in a time-dependent, high-magnitude increase in circulating thyroxine levels.

Animals↗
PubMed1987

Brain distribution of radioimmunoassayable gonadotropin-releasing hormone in female goldfish: seasonal variation and periovulatory changes.

A radioimmunoassay (RIA) for [Trp7, Leu8]gonadotropin-releasing hormone (sGnRH) was developed to determine the gonadotropin-releasing hormone (GnRH) content in discrete brain areas of female goldfish at different stages of ovarian development. Temporal changes in serum gonadotropin (GtH) and GnRH concentrations in discrete brain areas were measured during spontaneous ovulation. There were no clear parallel changes in brain GnRH with seasonal ovarian development in goldfish. However, under a 10 degrees temperature acclimation regimen, the GnRH content in the hypothalamus and pituitary decreased as the ovary progressed from the regressed to the mature condition; on the other hand. GnRH content in the spinal cord increased in sexually mature fish compared with that in regressed fish. Significant decreases in GnRH concentration were observed in certain brain areas (olfactory bulbs, telencephalon, hypothalamus, and pituitary) of fish undergoing spontaneous ovulation compared with those of nonovulatory fish. The simultaneous changes of GnRH concentration in these brain areas suggested that the GnRH neuronal system may function as an integrated unit for the activation of GtH secretion during ovulation in goldfish.

Animals↗
PubMed1987

Primary structure of common carp prolactins.

The complete amino acid sequence of common carp (Cyprinus carpio) prolactin (PRL) has been determined. One milligram of carp PRL was reduced, carboxymethylated, and then cleaved with cyanogen bromide and several enzymes. Another milligram of carp PRL was digested with lysyl endopeptidase. The resulting fragments were separated by reverse-phase high-performance liquid chromatography and subjected to sequence analysis by the automatic Edman method with a gas-liquid sequencer and the manual DNS-Edman method. The carp PRL consists of 186 amino acid residues with two disulfide linkages formed between residues 46-160 and 177-186. In addition, it lacks the linkage in the amino-terminal portion of mammalian prolactins, as do salmon and tilapia PRLs, and shows 77% sequence identity with salmon PRL and 36% identity with mammalian PRLs. The sequence comparison has been performed with 190 alignment positions. Four conserved segments of the alignment positions 1-32, 46-66, 71-94, and 155-182 that were found between salmon and mammalian PRLs are further confirmed in carp PRL. Variant residues are clustered in the region of residues 98-143 which has 48% sequence identity with salmon PRL and only 2% with mammalian PRL.

Amino Acid Sequence↗
PubMed1987

The influence of mammalian and teleost somatostatins on the secretion of growth hormone from goldfish (Carassius auratus L.) pituitary fragments in vitro.

The effect of various vertebrate somatostatins (SRIF) on basal growth hormone (GH) secretion from goldfish pituitary fragments was studied using an in vitro perifusion system. SRIF-14 caused a rapid and dose-dependent decrease in the rate of GH release from goldfish pituitary fragments. The half-maximal effective dose (ED50) of SRIF-14 was calculated as 1.3 nM following exposure to two minute pulses of increasing concentrations of SRIF-14, whereas the ED50 of SRIF-14 calculated after continuous exposure to sequentially increasing doses of SRIF-14 was 65 nM. This difference suggests that the pituitary fragments were less responsive to SRIF-14 in the latter experiment, possibly as a result of previous exposure to SRIF-14. SRIF-28 was found to be equipotent with SRIF-14 in decreasing basal GH secretion from the goldfish pituitary. In contrast, catfish SRIF-22, a uniquely teleost SRIF isolated from catfish pancreatic islets, did not alter GH secretion. These results provide further support for the hypothesis that SRIF-14 or a very similar molecule functions as a GH release-inhibiting factor in teleosts, indicating that this action of SRIF-14 has been fully conserved throughout vertebrate evolution.

Animals↗
PubMed1987

Characterization of gonadotropin-releasing hormone (GnRH) binding to pituitary receptors in goldfish (Carassius auratus).

Goldfish pituitary gonadotropin-releasing hormone (GnRH) receptors were characterized by using a superagonist analog of teleost GnRH (tGnRH-A; [D-Arg6, Trp7, Leu8, Pro9-NHEt]-GnRH). Equilibrium binding of 125I-tGnRH-A to a goldfish pituitary membrane preparation was achieved after a 30-min incubation at 4 degrees C; binding was significantly reduced after increasing incubation temperature to 22 degrees C. Binding of the radioligand was a function of tissue concentration, with a linear correlation over the range of 0.5-2 pituitary per tube. Incubation of the pituitary membrane preparation with increasing concentrations of 125I-tGnRH-A indicated saturable binding at radioligand concentrations of 470 pM and above. The binding of 125I-tGnRH-A was found to be reversible after addition of the cold analog, and the dissociation curve could be resolved into two linear components; slower rates of dissociation of 125I-tGnRH-A were observed after the addition of excess unlabeled tGnRH than after the addition of tGnRH-A, indicating that the analog is more effective in displacing the label than the native peptide. Addition of the cold analog displaced bound 125I-GnRH-A, and Scatchard analysis suggested the presence of at least two classes of binding sites: a high-affinity/low-capacity site and a low-affinity/high-capacity site. Bound 125I-GnRH-A was displaced by tGnRH from both sites in parallel to that observed with tGnRH-A, indicating that both peptides bind to the same classes of binding sites; however, tGnRH-A had a greater affinity for the receptors than the native tGnRH. These results demonstrated the presence and provided characterization of GnRH receptors in goldfish pituitary.

Animals↗
PubMed1987

Neuroanatomical substrate for the inhibition of gonadotrophin secretion in goldfish: existence of a dopaminergic preoptico-hypophyseal pathway.

To investigate the existence of a dopaminergic preoptico-hypophyseal pathway in the goldfish, electrolytic lesions were placed in the rostral preoptic area and their effects on gonadotrophin levels and pituitary innervation examined. In a first experiment, the fish were sacrificed 2 days after surgery and the pituitary studied by electron microscopy. Numerous exocytosis profiles were observed in the gonadotrophs, confirming the large increase in serum gonadotrophin levels measured in the animals. In addition, type A and B degenerating fibers were detected in the neurohypophysis and the pars distalis, in particular at the level of the gonadotrophs. In the second experiment, the distribution of tyrosine hydroxylase-immunopositive fibers was studied in the pituitary of controls and lesioned animals. It was found that lesioning the anterior ventral preoptic region resulted in the disappearance of all positive fibers in the pars distalis, while those in the neurointermediate lobe appeared unaffected. The presence of a large group of catecholaminergic perikarya in the destroyed area was confirmed in control animals. These results and other data strongly support the existence of a dopaminergic preoptico-hypophyseal pathway, providing a morphological support for the inhibitory effect of dopamine on the release of anterior pituitary hormones in teleosts, in particular gonadotrophin.

Animals↗
PubMed1987

In-vivo evaluation of dopamine receptor-mediated inhibition of gonadotrophin secretion from the pituitary gland of the goldfish, Carassius auratus.

Dopamine acts directly on the pituitary to modulate gonadotrophin (GtH) secretion in goldfish (Carassius auratus). In the light of this important role for dopamine in the regulation of goldfish reproduction, this investigation was designed to evaluate the receptor specificity of this dopamine inhibition and to describe the use of domperidone, a specific dopamine D2-receptor antagonist, in the manipulation of pituitary function in goldfish. To investigate the specificity of dopamine inhibition of GtH secretion, selected dopamine receptor antagonists were injected i.p. to block dopamine receptors thereby increasing GtH secretion as reflected by increased serum concentrations of GtH. Serum GtH levels were significantly increased by the active stereoisomer (-)-sulpiride in a dose-related fashion; (+)-sulpiride had no effect. Comparison of dopamine antagonists at low doses indicated that only domperidone and pimozide caused significant increases in serum concentrations of GtH. Dopamine antagonists potentiated the action of a gonadotrophin-releasing hormone analogue (GnRH-A) with an order of potency of domperidone = pimozide greater than metoclopramide = fluphenazine. [3H]Domperidone, injected i.p. with unlabelled domperidone, entered the blood and achieved maximum concentrations 12 h after injection, but did not accumulate in the brain in appreciable amounts. Gonadal 3H radioactivity was usually equal to or in excess of blood radioactivity, while [3H]domperidone was highly concentrated in the pituitary in a time-dependent fashion, with maximal accumulation occurring 24 h after injection. The time-course of pituitary accumulation of [3H]domperidone correlated well with the temporal increase in serum GtH levels in response to i.p. injected domperidone or domperidone plus an analogue of LHRH. Domperidone increased serum concentrations of GtH in a dose-related fashion; an analogue of salmon GnRH (sGnRH-A) increased the sensitivity and magnitude of the serum GtH response to domperidone. Serum concentrations of GtH were increased by sGnRH-A in a dose-related fashion; a low dose of domperidone substantially increased the sensitivity of the serum GtH response to sGnRH-A. These results indicate that dopamine inhibits GtH secretion from the goldfish pituitary by acting through a specific mechanism mediated by a dopamine D2 receptor. Domperidone increased serum concentrations of GtH, potentiated the action of gonadotrophin-releasing hormones and did not pass into the brain after i.p. injection into goldfish. The data also suggest that dopamine and GnRH, although acting through different receptors, influence the effect of each other on GtH release.

Animals↗
PubMed1986

Seasonal variations in body growth rates and circulating levels of growth hormone in the goldfish, Carassius auratus.

Several times throughout the year, changes in serum growth hormone (GH) levels over a 24-h period were determined in goldfish maintained under photoperiods and temperatures simulating natural (Edmonton) environmental conditions. In the goldfish a reproducible daily rhythm in circulating GH levels was not present at any time of the year. The average serum GH level over the daily sampling period and the instantaneous relative growth rate in goldfish sampled at the various times of the year were also determined. The highest mean daily serum GH levels were found in March and June, whereas the lowest level was found in goldfish sampled in November. Changes in mean daily serum GH levels were closely correlated to seasonal changes in daylength. The highest growth rate was found in goldfish sampled in July, whereas the lowest growth rates were found in February and March. Female goldfish exhibited a faster growth rate than male goldfish at certain times of the year, but sexual differences in growth rate were correlated with sexual differences in serum GH levels only in November when female goldfish had a higher serum GH level than male goldfish.

Aging↗
PubMed1986

A reinvestigation of the Gn-RH (gonadotrophin-releasing hormone) systems in the goldfish brain using antibodies to salmon Gn-RH.

The organization of Gn-RH systems in the brain of teleosts has been investigated previously by immunohistochemistry using antibodies against the mammalian decapeptide which differs from the teleostean factor. Here, we report the distribution of immunoreactive Gn-RH in the brain of goldfish using antibodies against synthetic teleost peptide. Immunoreactive structures are found along a column extending from the rostral olfactory bulbs to the pituitary stalk. Cell bodies are observed within the olfactory nerves and bulbs, along the ventromedial telencephalon, the ventrolateral preoptic area and the latero-basal hypothalamus. Large perikarya are detected in the dorsal midbrain tegmentum, immediately caudal to the posterior commissure. A prominent pathway was traced from the cells located in the olfactory nerves through the medial olfactory tract and along all the perikarya described above to the pituitary stalk. In the pituitary, projections are restricted to the proximal pars distalis. A second immunoreactive pathway ascends more dorsally in the telencephalon and arches to the periventricular regions of the diencephalon. Part of this pathway forms a periventricular network in the dorsal and posterior hypothalamus, whereas other projections continue caudally to the medulla oblongata and the spinal cord. Lesions of the ventral preoptic area demonstrate that most of the fibers detected in the pituitary originate from the preoptic region.

Animals↗
PubMed1986

Effects of [D-Ala6, Pro9-NEt]-LHRH and catecholaminergic drugs on gonadotropin secretion and ovulation in the Chinese loach (Paramisgurnus dabryanus).

The effects of [D-Ala6,Pro9-NEt]-LHRH (LHRH-A) alone and in combination with drugs which influence the actions of dopamine or the synthesis of catecholamines on gonadotropin (GtH) secretion and ovulation in the loach (Paramisgurnus dabryanus) were investigated. LHRH-A alone stimulated an increase in serum GtH levels in the loach, but was a relatively ineffective treatment for the induction of ovulation. Injection of the dopamine receptor antagonist pimozide caused a marked potentiation of the GtH-release response to LHRH-A, and combined injections of pimozide and LHRH-A were an effective treatment for the induction of ovulation. Reserpine, a drug which causes depletion of catecholamines from presynaptic terminals, also caused a marked potentiation of the GtH-release response to LHRH-A and combined treatment induced ovulation. Similarly, administration of alpha-methyl-para-tyrosine to block conversion of tyrosine to L-dopa, or carbidopa to block conversion of L-dopa to dopamine, potentiated the GtH-release response to LHRH-A and induced ovulation. In contrast, the use of diethyldithiocarbamate, to block conversion of dopamine to norepinephrine, failed to augment the action of LHRH-A on GtH release and ovulation. The present results provide further evidence to suggest that dopamine functions as a gonadotropin release-inhibitory factor in teleosts, and demonstrate that the use of drugs which block either the synthesis or the actions of dopamine potentiates the action of LHRH-A in teleosts.

Animals↗
PubMed1985

Elevations in gonadotrophin concentrations and milt volumes as a result of spawning behavior in the goldfish.

In many male mammals and birds, exposure to sexual stimuli results in acute elevations of circulating luteinizing hormone (LH) and testosterone (T); a similar phenomemon has now been observed in the male goldfish (Carassius auratus). Mature males placed with either a receptive female or stimulus pairs of spawning goldfish had gonadotrophin (GtH) concentrations and expressible milt (sperm) volumes that were significantly greater than those of males kept in all-male groups. This stimulatory effect lasted from 20 min to at least 2 hr for GtH (20 degrees) and from less than or equal to 1 hr to greater than or equal to 24 hr for milt (14 degrees). When males were separated from the spawning pair by either a solid or perforated clear partition, no elevations of GtH or milt levels occurred. In contrast, these values increased in males placed in contact with a spawning pair, even when that pair contained no female, but a male induced to perform female sexual behavior by treatment with prostaglandin. These results suggest that, in goldfish, access to a spawning situation is necessary for rapid elevations in GtH and milt. Furthermore, it appears that the males must be sexually active in order for these physiological changes to occur, as males that failed to engage in courtship behavior with a spawning pair had GtH and milt values not different from isolated fish. This suggests that male sexual behavior and elevations in milt and GtH are concurrent events that share a common activation pathway in the brain. The increase in milt may be due to both neurally and hormonally mediated events that ensure milt availability for imminent spawning activity.

Animals↗
PubMed1985

Seasonal effects of pimozide and des Gly10 [D-Ala6] LH-RH ethylamide on gonadotrophin secretion in goldfish.

The seasonal changes in the gonadotrophin-release-inhibitory activity of dopamine and responsiveness to gonadotrophin-releasing hormone were investigated by determining the effects of injection of pimozide, a dopamine receptor antagonist, des-Gly10 [D-Ala6] LH-RH ethylamide (LRH-A), or the combination of pimozide plus LRH-A on serum gonadotrophin (GtH) levels of goldfish, held at 12 or 20 degrees C, at different stages of gonadal development. As in previous studies, pimozide greatly potentiated the GtH-release response to LRH-A. The highest concentrations of serum GtH induced by injection of pimozide or LRH-A alone, or the combination of pimozide plus LRH-A were in females in late stages of ovarian recrudescence; fish that were sexually regressed (males and females combined) were the least responsive, and fish that were in early stages of gonadal recrudescence, and mature females ( = prespawning, completed ovarian recrudescence) were intermediate. Fish held at 20 degrees C had a more rapid onset of GtH release and had higher serum GtH levels initially compared to fish at 12 degrees C at similar sexual stages; however, the fish held at 12 degrees C generally had a more prolonged increase in serum GtH levels, indicating that temperature influence the time course of the GtH-release response. The results indicate that there is a seasonal variation in responsiveness to injection of pimozide, LRH-A and the combination of pimozide plus LRH-A. These seasonal changes may be due to differences in the pituitary content of GtH, the ability of the pituitary to synthesize GtH, or changes in GtH cell receptors for GnRH and dopamine, or a combination of these and other unknown factors.

Animals↗