Biomedical subjects
Publications and source records attributed to R E Peter.
This case report describes an unusual arthroscopic finding in a patient presenting with typical symptomatology of a medial meniscal tear of the right knee. Arthroscopy showed an multilobulated tumor that on histological examination was diagnosed as an intraarticular Schwannoma.
In goldfish, GnRH stimulates gonadotropin-II (GTH-II) and growth hormone (GH) release. The two native forms of GnRH, salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), bind to two classes of GnRH binding sites: high-affinity/low-capacity sites and low-affinity/high-capacity sites. Our previous in vitro perifusion studies of goldfish pituitary fragments showed that [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6]-mGnRH (analog E), [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6]-sGnRH (analog C), and [Ac-D(2)Nal1, 4Cl-D-Phe2, D-(3)Pal3,6]-cGnRH-II (analog N) inhibited both sGnRH- and cGnRH-II-stimulated GTH-II and GH release. Interestingly, analog C stimulated GH release but not GTH-II release. The objectives of the present study were 1) to test the site of action of GnRH antagonists in goldfish, 2) to test the relationship between receptor binding affinity of antagonists and their in vitro inhibitory potencies and apparent duration of action, and 3) to compare the binding characteristics of analog C with its differential action on GTH-II and GH release. As in previous studies, analog E suppressed sGnRH-stimulated GTH-II and GH release from perifused pituitary fragments. Similarly, analog E suppressed both sGnRH- and cGnRH-II-stimulated GTH-II and GH release from perifused dispersed goldfish pituitary cells, indicating the direct action of GnRH antagonists at the pituitary cell level. In the receptor binding studies, analog E displaced 125I-[D-Arg6, Pro9NHEt]-sGnRH (sGnRH-A) from crude goldfish pituitary membrane preparations in a dose-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)
This biomechanical study compares two methods of internal fixation of the tibiofibular syndesmosis used in Weber type C malleolar fractures of the ankle. The transverse syndesmotic 3.5-mm screw was compared with two 1.5-mm Kirschner wires introduced obliquely across the distal tibiofibular syndesmosis. The influence of implants on distal tibiofibular joint motion and contact characteristics of the intact ankle joint were determined. Up to 1.25 mm of lateral displacement and 2 degrees of external rotation of the lateral malleolus during uninjured ankle dorsiflexion was recorded. Both techniques stabilized the injured syndesmotic joint and limited its normal motion during flexion and extension of the ankle. Pressure distribution displaced laterally in internally stabilized ankles compared with intact specimens, regardless of the type of fixation used. Therefore, both techniques alter joint biomechanics equivalently compared with the intact ankle.
The presence and distribution of cholecystokinin (CCK)/gastrin-like immunoreactive (IR) material were examined in the goldfish brain and gut. In the forebrain, CCK/gastrin-like IR fibers and perikarya were localized to nuclei of predominantly the ventral telencephalon and diencephalon; more dorsal forebrain regions contained only few, thin-beaded, sparsely distributed IR fibers. CCK/gastrin-like IR was specifically detected in the preoptic hypothalamus, including the nucleus entopeduncularis, nucleus preopticus periventricularis, and nucleus preopticus. Of all brain regions examined, the highest concentration of CCK/gastrin-like IR staining was consistently observed in nuclei of the ventroposterior and inferior lobes of the hypothalamus. Within the gut, both nerve fibers and endocrine cells contained CCK/gastrin-like IR. The abundance of CCK/gastrin-like IR material within brain areas known to represent the feeding center of fish, as well as the presence of IR material within the gut, suggests that CCK may influence feeding behavior in fish. When injected either intraperitoneally or into the third brain ventricle into goldfish, sulfated CCK-8 (CCK-8s) suppressed food intake. The nonsulfated form of CCK-8 was not as effective as CCK-8s in suppressing feeding after intraperitoneal injection. No consistent changes were observed in circulating serum growth hormone or gonadotropin levels after either intraperitoneal or intracerebroventricular injection of CCK-8s. These studies demonstrate for the first time that CCK-8s is effective in acutely suppressing feeding behavior in fish when administered either peripherally or centrally into the third brain ventricle.
In goldfish the two native forms of gonadotropin-releasing hormone (GnRH), salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), stimulate both gonadotropin-II (GTH-II) and growth hormone (GH) release. Modifications of GnRH structure at positions 1, 2, 3, and 6 often result in an antagonist in goldfish, an observation well documented in mammalian studies. In a preliminary study in goldfish, a mammalian GnRH antagonist, [Ac-D(2)Nal1, 4Cl-D-Phe2, D(3)-Pal3,6, Arg5, D-Ala10]-mGnRH (analog L) weakly stimulated GTH-II release, and strongly inhibited GH release. The objectives of the present study were to study the dose-related actions of analog L on GTH-II and GH release in the goldfish, the specificity of inhibition of native GnRH actions, and to test whether analog L can act directly on goldfish pituitary cells. In a goldfish pituitary fragments perifusion system, analog L at different concentrations, given as 2-min pulses or as 30-min prolonged treatments, stimulated GTH-II and inhibited GH release in a dose-dependent manner. Analog L at 2 microM concentration (45 min) significantly suppressed sGnRH- and cGnRH-II-stimulated GTH-II as well as GH release. Analog L specifically inhibited GnRH-stimulated GH release, without having any significant effects on the GH release induced by either SKF38393, a dopamine D1 receptor agonist, or thyrotropin-releasing hormone. The GTH-II stimulatory and GH-inhibitory actions of analog L were significantly suppressed by a 'true' GnRH antagonist (Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6)-mGnRH. Further, analog L stimulated GTH-II release and suppressed GH release from the enzymatically dispersed goldfish pituitary cells, indicating the direct actions of analog L at the pituitary cell level. Analog L also displaced 125I-(D-Arg6, Pro9 NHEt)-sGnRH bound to crude goldfish pituitary membrane preparations in a dose-related manner. In conclusion, contrary to its action as a potent GnRH antagonist in mammals, analog L has GTH-II stimulatory action in goldfish. Analog L by acting via GnRH receptors at the pituitary cell level differentially acts on GTH-II and GH release, suggesting functional differences in the properties of the GnRH receptors on GTH and GH cells. Analog L also specifically inhibits sGnRH and cGnRH-II actions on GTH-II and GH release.
Neuropeptide-Y (NPY) has been recently cloned from a goldfish cDNA library. Using a probe derived from this cDNA clone, the distribution and regulation of NPY mRNA in the goldfish brain were examined in the present study by in situ hybridization, Northern blot analysis, and ribonuclease protection assay. Frozen tissue sections from the goldfish brain and pituitary were hybridized with a digoxigenin-labeled RNA probe. Hybridization signal was detected mainly in fore-brain regions, particularly in the nucleus entopeduncularis of the ventral telencephalon, the preoptic area (POA), the olfactory bulbs, and various thalamic regions. In the midbrain, NPY mRNA was found in the optic-tectum and locus coeruleus. Northern blot hybridization of total RNA extracted from different brain areas with a 32P-labeled RNA probe detected a single mRNA species and confirmed that most NPY mRNA was present in telencephalon/POA and optic-tectum/thalamus. Our previous physiological studies showed that the ovarian steroids testosterone (T) and estradiol (E2) have potentiating effects on the actions of NPY on gonadotropin and GH release. Therefore, we also tested the possibility that T and E2 may modulate NPY gene expression. Fish were implanted ip with pellets containing T, E2, or no steroid (control) for 5 days, RNA was extracted, and NPY mRNA levels were estimated using a ribonuclease protection assay. Pretreatment with T or E2 induced a 2- to 3-fold increase in NPY mRNA levels in the telencephalon/POA, but not in the optic-tectum/thalamus. In situ hybridization using brains taken from T-implanted fish demonstrated that the site of steroid action is the POA. This report represents the first study on NPY gene expression in a nonmammalian species and demonstrates that 1) NPY mRNA is present in the neuroendocrine regulatory centers; and 2) ovarian steroids stimulate NPY gene expression in the POA.
It is known that norepinephrine (NE) is important in the neuroendocrine control of pituitary gonadotropin II (GTH-II) and growth hormone (GH) release but very little is known about the factors regulating NE neurons in the goldfish brain. Female gonad-intact goldfish were implanted intraperitoneally (100 micrograms/g) with testosterone (T) or estradiol (E2) to elevate serum steroid levels. High-performance liquid chromatography measurements showed that steroid implantation had no effect on NE content in the telencephalon, including preoptic area (TEL-POA), or the hypothalamus (HYP). The turnover rate of NE was estimated from the rate of depletion of NE content from tissues following inhibition of tyrosine hydroxylase by alpha-methyl-p-tyrosine (240 micrograms/g). The present study demonstrates that E2 can decrease NE turnover rates in TEL-POA and HYP of sexually regressed goldfish (August). The results in recrudescent fish (November), however, indicate a more complex interaction of E2 with NE neurons since E2 increased NE turnover in TEL-POA and HYP in these animals. Testosterone (T) has less prominent effects on NE turnover rates in TEL-POA and HYP; the only significant effect of T-implantation was a small reduction of NE turnover in the TEL-POA of sexually recrudescent fish. Elevation of endogenous brain GABA concentrations by injection of the GABA transaminase inhibitor, gamma-vinyl-GABA (300 micrograms/g), significantly reduced NE turnover in TEL-POA. These data demonstrate that goldfish NE neurons in the TEL-POA are sensitive to regulation by changes in circulating sex steroids and by increases in brain GABA.
Inhibin and activin are structurally related dimeric peptides sharing two distinct but related subunits, beta A and beta B. By using polymerase chain reaction (PCR), we have cloned and sequenced activin beta A and beta B genes encoding the mature region of the peptides from the goldfish genomic DNA. A single form of beta A and two forms of beta B subunits were found. There is high identity with mammalian counterparts; the goldfish beta A subunit has 78% protein sequence identity with human beta A subunit, and the two beta B subunits have more than 94% sequence identity with human beta B subunit. This is the first demonstration of the activin family of peptides in the fishes.
In goldfish it is known that intraperitoneal implantation with testosterone (T) or estradiol (E2) potentiates the serum gonadotropin-II (GtH-II) response to gonadotropin-releasing hormone (GnRH) without affecting basal GtH-II levels. Since the release of GtH-II in goldfish is under a tonic dopaminergic inhibitory tone, the possibility of sex steroids modulating brain and pituitary dopamine was examined in vivo and in vitro. Implantation of females with either T or E2 (100 micrograms/g in solid silastic pellets) also potentiated the increase in serum GtH-II in response to the dopamine antagonist, domperidone (10 micrograms/g). High-performance liquid chromatography measurements showed that steroid implantation had no effect on dopamine content in the telencephalon including preoptic area, hypothalamus, and pituitary. However, the present study demonstrates that T or E2 can increase pituitary dopamine turnover rates following tyrosine hydroxylase inhibition with alpha-methyl-p-tyrosine (240 micrograms/g). In vitro perifusion of pars distalis fragments from E2- or T-treated fish also showed a potentiation of salmon GnRH (sGnRH)-induced GtH-II release compared to controls. However, exposure to pituitary fragments from control and steroid-treated fish to increasing doses of the dopamine agonist LY 171555 did not demonstrate a significant difference in the sensitivity of the gonadotrophs to dopamine. Testosterone-induced alterations in DA turnover are dissociable from the positive action of T on pituitary responsiveness, since the potentiating effect of T implantation was not affected by severe depletion of brain and pituitary DA levels by alpha-methyl-p-tyrosine pretreatment. These data demonstrate that in gonad-intact goldfish, sex steroids enhance pituitary responsiveness to GnRH but basal serum GtH-II levels are maintained by a concomitant increase in DA turnover in the pituitary.
The effects of salmon gonadotropin-releasing hormone (sGnRH) and the superactive agonist [D-Arg6, Pro9NEt]-sGnRH (sGnRH-A) on growth hormone (GH) and gonadotropin (GtH) release were examined using a perifusion system for pituitary fragments of the common carp (Cyprinus carpio). Perifusion of 2-min pulses of different concentrations of sGnRH or sGnRH-A stimulated a rapid and dose-dependent increase in GH release: ED50 values for sGnRH and sGnRH-A in stimulating GH release were 2.8 +/- 0.7 and 0.5 +/- 0.1 nM, respectively, indicating that the superactivity of sGnRH-A for stimulation of GtH release also applies in induction of GH release. Exposure of the pituitary fragments to 10 nM sGnRH or sGnRH-A alone resulted in increases in GH and GtH release on a similar temporal course. Apomorphine (10, 100, and 1000 nM) significantly inhibited basal and GnRH-induced GtH release in a dose-dependent manner and significantly stimulated basal GH release; however, APO did not enhance GnRH-induced GH release. Somatostatin (100 nM) significantly blocked basal release and 10 nM sGnRH- and sGnRH-A-induced GH release, but was ineffective on GtH release. Treatment with somatostatin (100 nM) in combination with apomorphine (100 nM) caused an increase in sGnRH-induced GH release compared to treatment with somatostatin alone; whereas, on GtH there was a significant decrease in basal and GnRH-induced levels, compared to treatment with somatostatin alone. These results indicate that GH release in common carp is regulated by somatostatin as GH release inhibitor. sGnRH and sGnRH-A act as GH-releasing factors; the mechanisms by which GnRH stimulates GH and GtH secretion are independent. The dopamine agonist apomorphine stimulates GH release and inhibits GtH release directly at the pituitary level.
In previous studies, we have demonstrated that inhibin and activin are stimulatory to goldfish gonadotropin release. In the present study, the distribution of immunoreactive inhibin and activin subunits (alpha, beta A, and beta B) in goldfish gonads was examined with domain-specific antibodies against mammalian inhibin and activin subunits, using the avidin-biotin-peroxidase complex method. In the ovary, follicle cells surrounding the oocyte were heavily stained with anti-porcine beta A and human beta B subunits. The cytoplasm of previtellogenic oocytes, at all stages of the ovarian cycle, also showed strong reactions with anti-beta A and beta B. As ovarian recrudescence progressed, oocytes that started to accumulate cortical vesicles gradually lost their immunoreactivity, with the reaction intensity inversely proportional to the amount of cortical vesicles in the oocyte; when oocytes became full of cortical vesicles, the oocytoplasm was no longer immunoreactive to anti-beta A and beta B. The staining with antiporcine alpha subunit was similar to that with anti-beta A and beta B but the reaction intensity was weaker than that with anti-beta A and beta B. In the testis, the mature sperm in the tubular lumen exhibited a strong immunoreaction to anti-alpha antibody, while the interstitial tissue was completely negative. However, the immunoreactivities with anti-beta A and beta B in the testis were exclusively restricted to the interstitial tissues. These results provide evidence for the presence of inhibin and activin-like molecules in the goldfish and reveal the distribution of these molecules in the goldfish gonads.
Neuropeptide Y (NPY) has been recently characterized in the goldfish and the sequence deduced from goldfish brain cDNA clones reveals that goldfish NPY (gNPY) has over 86% identity with human NPY (hNPY) (Blomqvist et al., 1992, Proc. Natl. Acad. Sci. USA 89, 2350-2354). In the present study, we used synthetic gNPY to investigate the role of NPY in the regulation of growth hormone (GH) and gonadotropin-II (GtH-II) in the goldfish. The dose-response relationships of gNPY on GH and GtH-II release were first tested using an in vitro perifusion system for pituitary fragments. It was found that gNPY stimulated both GH and GtH-II release in a dose-dependent manner, with ED50 values of 1.89 +/- 0.9 nM for GH and 4.19 +/- 2.9 nM for GtH-II. In addition, the C-terminal fragment gNPY (18-36) stimulated the release of both GH and GtH-II, but with lower potency than did the intact molecule. These results confirm our previous findings using hNPY. The interactions of gNPY and other GH and GtH-II regulators were also examined in the present studies. Prolonged infusion of sGnRH induced initial peak releases of GH and GtH-II, followed by a second phase of sustained hormone release at a reduced level. Application of a 5-min pulse of gNPY during the second phase of sGnRH action further stimulated GH and GtH-II release, but only to the levels similar to those induced by gNPY alone. Prolonged infusion with gNPY induced a rapid desensitization of GH and GtH-II release; the hormone levels returned to basal within 25 min in the continued presence of gNPY. Administration of 5-min pulse of sGnRH during the desensitization phase of continuous gNPY perfusion induced a similar GH response to that induced by sGnRH alone, whereas the GtH-II responses to sGnRH given during gNPY infusion were smaller than the responses to sGnRH alone, suggesting that the mechanisms of gNPY stimulation on GH and GtH-II release may be somewhat different. The gNPY-induced GH release was blocked by somatostatin, a known GH inhibitor; the gNPY-induced GtH-II release was reduced by dopamine, a known inhibitor for GtH-II. Finally, intraperitoneal injection of gNPY induced time- and dose-dependent increases in serum GH and GtH-II levels. Together, these results suggest that NPY may play a physiological role in the regulation of GH and GtH-II secretion in the goldfish.
The presence and distribution of cholecystokinin (CCK)/gastrin-like immunoreactivity (IR) was examined in the goldfish pituitary. Intense CCK/gastrin-like IR was consistently observed within fibers of the proximal pars distalis (PD), with fewer IR fibers localized in the rostral PD. Within the proximal PD CCK/gastrin-like IR fibers were distributed among both the gonadotrophs and somatotrophs, suggesting a possible role for CCK-like peptides in the regulation of gonadotropin-II (GtH-II) and growth hormone (GH) secretion. Exposure of pituitary fragments from either sexually gonadal recrudescing (maturing) or regressed goldfish to three 5-min pulses of 1.0 or 10 nM sulfated CCK8 (CCK8-s), at 55-min interpulse intervals, resulted in an increased secretion of both GtH-II and GH. Independent of the dose perifused, the GtH-II release responses to the second and third pulses of CCK8-s were always of similar magnitude to the first pulse at a given dose. For GH, repeated challenges of pituitary fragments to 0.1 or 1.0 nM CCK8-s stimulated release responses of similar magnitude; however, successive pulses of 10 nM CCK8-s resulted in a desensitization in the GH release response to the second or the third pulse. Fragments from sexually regressed goldfish exhibited an overall greater release response of GtH-II to CCK8-s relative to fragments from sexually recrudescing fish, whereas the GH release responses to CCK8-s were similar between the two sexual stages. A dose-dependent release of GtH-II was present in pituitary fragments from sexually regressed goldfish following five 5-min pulses of increasing (0.1 to 100 nM) doses of CCK8-s. Finally, the sulfated forms of CCK8 and gastrin 17 (G17-s) exhibited greater stimulatory abilities than the nonsulfated form of CCK8 in releasing GtH-II and GH from fragments of sexually recrudescing fish. Additionally, CCK8-s and G17-s were equal in their capacity to stimulate the release of GtH-II, whereas G17-s was slightly more effective than CCK8-s in stimulating the release of GH. Overall, these studies are the first to provide evidence that IR CCK/gastrin-like fibers are codistributed among the gonadotrophs and somatotrophs, and that CCK-like peptides are highly effective in stimulating GtH-II and GH release from the goldfish pituitary.
Previously, we have demonstrated that dopamine (DA) stimulates growth hormone (GH) release from the goldfish pituitary through DA D1 receptors. In the present study, the role of DA as a GH-releasing factor was further examined in vitro by studying its interactions with other GH regulators in the goldfish. The GH-releasing effects of DA and salmon gonadotropin-releasing hormone (sGnRH) were found to be independent and additive at the pituitary cell level. Both the kinetics and the magnitude of DA-stimulated GH release were unaffected by simultaneous treatment with sGnRH and vice versa. Castration of sexually mature (or prespawning) goldfish significantly enhanced the DA-stimulated GH release, but at the same time reduced the GH responses to sGnRH. Furthermore, the GH responses to DA and the D1 agonist SKF38393 were totally abolished by somatostatin (SRIF), a known GH release inhibitor in the goldfish. These findings strongly indicate that SRIF, DA, sGnRH, and gonadal factors interact at the pituitary level to regulate GH release in the goldfish.
The generation of intramedullary pressure during reaming of the femur was compared for two different reamer systems: the AO/ASIF universal reamer and the Gray flexible reamer system (Howmedica), while reaming in 9 oncologic patients undergoing prophylactic nailing of metastatic femora as indicated by impending fractures (unbroken femora). An intracranial fibre optic catheter pressure-monitoring device inserted through the distal supracondylar cortex was used to perform measurements. Preliminary data are presented. Maximum pressures of up to 450 mmHg were recorded during reaming with the smaller 9.0 and 9.5 mm theta reamers. Rapid penetration of the reamer in both proximal and distal metaphyses caused much higher pressures than reaming the cortex of the diaphysis. Speed of penetration and volume of the reaming shaft were found to be important parameters. No significant differences between maximal pressures generated by the two types of reamers could be observed.
The effects of gonadal steroids on the gonadotropin (GTH) release response to salmon gonadotropin-releasing hormone (sGnRH), chicken gonadotropin-releasing hormone-II (cGnRH-II), and the sGnRH analogue, [D-Arg6, Trp7, Leu epsilon, Pro9]-N-ethylamide-GnRH (sGnRH-A), were investigated using an in vitro perifusion system for goldfish pituitary fragments. Gonad-intact male and female goldfish were implanted intraperitoneally (i.p.) with silastic pellets containing no steroid (blank), testosterone (T; 100 micrograms/g), or estradiol (E2; 100 micrograms/g); pituitaries were removed 5 days later for perifusion experiments. In vivo treatment with T or E2 potentiates sGnRH-, cGnRH-II-, and sGnRH-A-induced GTH secretion from pituitary fragments of sexually regressed and sexually recrudescent goldfish in vitro. Testosterone (100 nM; 24 h) treatment in vitro has a direct effect on the pituitary to increase sGnRH responsiveness, and this potentiating effect of T was blocked by the protein synthesis inhibitor cycloheximide (25 microM). In sexually regressed goldfish, in vivo T implantation enhanced the serum GTH response to sGnRH-A (0.01 microgram/g; 6 h) 7-fold. ED50 estimates for in vitro pituitary GTH responsiveness to sGnRH-A were 1.0 +/- 0.1 nM and 0.1 +/- 0.1 nM (p < 0.05) for blank and T-implanted groups, respectively. Radioligand (125I-sGnRH-A) binding studies demonstrated that enhanced pituitary responsiveness was independent of changes in pituitary GnRH receptor affinity or number. These results demonstrate that sex steroids increase pituitary sensitivity to GnRH peptides in the goldfish.
The effects of gonadal steroids on GABA-, taurine (TAU)- and N-methyl-D,L-aspartate (NMA)-induced gonadotropin-II (GTH-II) release were investigated in male and female goldfish in vivo. In sexually regressed goldfish (both sexes mixed), intraperitoneal implantation for 5 to 10 days with solid Silastic pellets containing testosterone (100 micrograms/g), oestradiol (100 micrograms/g) or progesterone (100 micrograms/g) was previously shown to elevate serum sex steroid levels to values comparable to those in sexually mature animals, and to potentiate gonadotropin-releasing hormone-stimulated GTH-II release. In the present study, testosterone but not oestradiol or progesterone enhanced the stimulatory effects of exogenous GABA (100 micrograms/g) on GTH-II release in vivo. TAU (1 mg/g) stimulated GTH-II release in sexually regressed mixed sex and sexually recrudescent male goldfish, and both testosterone and oestradiol implantation enhanced GTH-II release induced by TAU. The glutamate agonist NMA (25 to 50 micrograms/g) was also found to stimulate GTH-II release; however it was relatively less effective in elevating serum GTH-II levels than GABA and TAU, and its effects were not modulated by sex steroid treatments. Pretreatment of goldfish with alpha-methyl-p-tyrosine to deplete brain and pituitary catecholamines did not affect NMA action on GTH-II release. Our results indicate that GABA, TAU and NMA are involved in the neuroendocrine regulation of GTH-II release in goldfish, and support the idea that testosterone participates in the positive feedback regulation of pituitary gonadotropin release in a non-mammalian vertebrate by enhancing GABA- and TAU-stimulated GTH release in vivo.
The effects of neuropeptide Y (NPY) on growth hormone (GH) and gonadotropin-II (GtH-II) release in different reproductive stages were studied using perifused pituitary fragments of female goldfish. The GH and GtH-II release responses to 5-min pulses of NPY were relatively small in sexually regressed fish (July), intermediate in recrudescent fish (December), and maximal in sexually mature (= prespawning) fish (May). To test if sex steroids can modulate NPY action, the effects of in vivo implantation of 17 beta-estradiol (E2) and testosterone (T) (both at 100 micrograms/g dosage) on NPY-induced GH and GtH-II secretion were examined. In sexually regressed goldfish, implantation of T significantly enhanced NPY-induced GH and GtH-II release from perifused pituitary fragments; implantation of E2 potentiated the NPY-induced GtH-II, but not GH release. However, steroid implantation did not affect responses to NPY when this experiment was repeated using pituitaries from sexually mature fish. To test the hypothesis that steroids may act directly at the level of the pituitary to potentiate NPY action, pituitary fragments taken from sexually regressed goldfish were incubated with 100 nM T for 24 h, and the GH and GtH-II responses to 5-min challenges of NPY assessed in the presence of T. Both GH and GtH-II responses to NPY were not affected by treatment with T in vitro, suggesting that T does not act directly at the level of the pituitary.(ABSTRACT TRUNCATED AT 250 WORDS)