Tc-99m albumin scintigraphy to monitor the effect of treatment in protein-losing gastroenteropathy

PURPOSE

Tc-99m albumin scintigraphy is a noninvasive method for detecting protein-losing gastroenteropathy.

METHODS

Seven patients with protein-losing gastroenteropathy were evaluated with Tc-99m albumin scintigraphy. In addition, Tc-99m albumin scintigraphy was used to monitor the effect of treatment in five of these seven patients. The scintigraphic results were compared with serum albumin levels.

RESULTS

All seven patients had positive results in the pretreatment images. Changes in scintigraphic findings in the five treated patients correlated well with changes in serum albumin level.

CONCLUSION

Tc-99m albumin scintigraphy is useful not only for diagnosing protein-losing gastroenteropathy but also for monitoring the effect of treatment.

Lymphoscintigraphy using larger colloid particles may enhance visualization of the sentinel node in breast cancer: a case report

Lymphoscintigraphy along with a gamma-detecting probe has been applied successfully to breast cancer patients to localize the sentinel node during surgery, with a 5% false-negative rate. The authors report a case of stage II breast cancer. The sentinel node was not visualized on the initial lymphoscintigraphy with peritumoral injection of 37 MBq (1 mCi) 10 ml Tc-99m colloidal rhenium sulfide (Tc-99m ReS colloid; average particle size, 100 nm). However, the sentinel node was visualized in the left lateral view of the second lymphoscintigraphy with peritumoral injection of 37 MBq (1 mCi) 10 ml Tc-99m ReS colloid (average particle size, 500 nm). Lymphoscintigraphy using the larger colloid particles may enhance visualization of a sentinel node in breast cancer.

Quickly predicting chemotherapy response to paclitaxel-based therapy in non-small cell lung cancer by early technetium-99m methoxyisobutylisonitrile chest single-photon-emission computed tomography

The purpose of this study was to retrospectively predict the chemotherapy response to paclitaxel in non-small cell lung cancer (NSCLC) using technetium-99m methoxyisobutylisonitrile (Tc-99m MIBI) chest single-photon-emission computed tomography (SPECT) to detect the expression of multidrug-resistance-mediated Mr 170,000 P-glycoprotein. Before chemotherapy with Paclitaxel (Taxol), 30 patients with stage IIIb or IV NSCLC were enrolled in this study. Early chest SPECT 10 min after i.v. injection of Tc-99m MIBI was performed to qualitatively interpret Tc-99m MIBI chest SPECT visually and quantitatively calculate early tumor:normal lung ratios (T:NL) for quick assessment of multidrug-resistant P-glycoprotein expression in NSCLC. On the basis of qualitatively visual interpretation of early Tc-99m MIBI chest SPECT, all of 15 (100%) cases with good response to chemotherapy with Taxol could be detected but 10 (67%) of 15 cases with poor response could not be detected. Early Tc-99m MIBI chest SPECT could correctly predict chemotherapy response in 25 (83%) of 30 of cases. The early T:NL were 3.30 +/- 0.82 for 15 patients with good response and 2.02 +/- 0.19 for 5 patients with poor response. The differences were significant (P < 0.05) by independent Student t tests. However, no significant differences were found for other prognostic factors (age, sex, tumor size, tumor location, stage, and cell type) between good-response and poor-response patients. Early Tc-99m MIBI chest SPECT has the potential to predict chemotherapy response to Paclitaxel.

Simian virus 40 large T antigen binds a novel Bcl-2 homology domain 3-containing proapoptosis protein in the cytoplasm

A 193-kDa SV40 large T antigen (T-Ag)-binding protein, designated p193, was identified and cloned. Inspection of the deduced amino acid sequence revealed the presence of a short motif similar to the Bcl-2 homology (BH) domain 3, suggesting that p193 may be a member of a family of apoptosis promoting proteins containing only BH3 motifs. In support of this, p193 expression promoted apoptosis in NIH-3T3 cells. Deletion of the BH3 motif abolished p193 apoptosis activity. p193-induced apoptosis was antagonized by co-expression of Bcl-X(L). Immune cytologic analysis indicated that p193 is localized to the cytoplasm of transfected cells. p193-induced apoptosis was also antagonized by co-expression of T-Ag, which resulted in the cytoplasmic localization of both proteins. The p193 binding site was mapped to an N-terminal region of T-Ag previously implicated in transforming activity. These results suggest that T-Ag possesses an antiapoptosis activity, independent of p53 sequestration, which is actuated by T-Ag/p193 binding in the cytoplasm.

Age-related differences in the secretion of calcitonin in male rats

The mechanism of hypercalcitoninemia associated with aging was investigated in male rats. To mimic some of the hormonal changes with aging, orchidectomized (Orch) and hyperprolactinemic rats were used to mimic the physiological status of aging. Orch and haloperidol-induced hyperprolactinemic rats aged 3, 8, and 17 months were infused with CaCl2 and then bled from a jugular catheter following the CaCl2 challenge. Rat thyroid gland was incubated with Locke's medium at 37 degrees C for 30 minutes. Compared with 8- and 3-month-old rats, 17-month-old rats exhibited the lowest levels of plasma testosterone and the highest levels of plasma prolactin (PRL) and calcitonin (CT). The release of CT in the thyroid glands in vitro was highest in 17-month-old rats. Orchidectomy decreased rat plasma CT and thyroid CT release in vitro. Hyperprolactinemic rats had higher levels of plasma PRL and CT compared with control animals. The release of thyroid CT in vitro was greater in hyperprolactinemic rats. These results suggest that the hypersecretion of CT in 17-month-old rats may be due in part to hyperprolactinemia.

A comprehensive study on the blockage of thyroid and gastric uptakes of 188Re-perrhenate in endovascular irradiation using liquid-filled balloon to prevent restenosis

188Re-perrhenate has been reported effective in preventing restenosis after percutaneous transluminal coronary angioplasty. However, if the balloon ruptures, 188Re-perrhenate is released into the circulation, causing high radiation dosing to the thyroid and stomach. In this study, we evaluated the effects of perchlorate or iodide given at different times and in different ways for blocking the uptake of 188Re-perrhenate in the thyroid glands and the stomach to find the best method to apply clinically to reduce the radiation dose in case of balloon rupture. Sodium perchlorate, sodium iodide, or potassium iodide was given orally or intravenously to rats before, during, and after the injection of 188Re-perrhenate. The rats were sacrificed and we calculated the concentration of 188Re-perrhenate in various organs to evaluate the preblocking, mixed formula, and postblocking effects of perchlorate or iodide. Our data showed that the preblocking method effectively reduced the uptake of 188Re-perrhenate in both the thyroid and the stomach. The mixed formula method also demonstrated good blocking effect. The postblocking method showed obvious depression of thyroid uptake of perrhenate but its blocking effect on the stomach was not satisfactory.

Evaluation of three rhenium-188 candidates for intravascular radiation therapy with liquid-filled balloons to prevent restenosis

BACKGROUND

Intravascular brachytherapy is an effective method for inhibiting coronary restenosis after percutaneous transluminal coronary angioplasty. A new concept for preventing restenosis is the use of a liquid-filled balloon containing a beta-ray-emitting radioisotope. Generator-produced rhenium-188 (Re-188) is a good candidate for intravascular brachytherapy. However, in the unlikely event of balloon rupture, release of Re-188 perrhenate may cause a high radiation dose to the thyroid and stomach. In this study, we compared the biodistributions of three Re-188 preparations (Re-188 perrhenate, Re-188 pentetic acid [DTPA], and Re-188 MAG3) to assess the radiation dose to organs in a rat model that mimicked balloon rupture.

METHODS AND RESULTS

After injection of Re-188 preparations intravenously, rats were killed at 10 minutes, 30 minutes, 60 minutes, 2 hours, and 6 hours (n = 5/group). Tissue concentrations were calculated and expressed as percent injected dose per gram or per milliliter. In addition, urine excretion and thyroid gland uptake were evaluated in rats (n = 5/group) with a gamma camera after administration of 37 MBq (1 mCi) of each agent. Our data showed all 3 agents were excreted primarily via urine. In the Re-188 MAG3 group, 82% was excreted within 1 hour, but in the Re-188 perrhenate group, only 28% was excreted. The biodistribution data for these agents revealed that radioactivity levels in the stomach and the thyroid gland were high in the perrhenate group but low in the Re-188 DTPA and Re-188 MAG3 groups. The concentration levels in other tissues including lung, liver, testis, muscle, and blood were low throughout this study for all 3 agents. The thyroid radiation values were 0.163, 0.0167, and 0.00728 mGy/MBq for Re-188 perrhenate, Re-188 DTPA, and Re-188 MAG3, respectively. The stomach radiation values were 0.127 mGy/MBq for Re-188 perrhenate, 0.013 mGy/MBq for Re-188 DTPA, and 0.0104 mGy/MBq for Re-188 MAG3.

CONCLUSIONS

In the event of balloon rupture, the release of Re-188 MAG3 or Re-188 DTPA results in lower radiation doses than release of Re-188 perrhenate, especially to the thyroid gland and the stomach.

Effects of butter and soybean oils on solid-phase gastric emptying in patients with functional dyspepsia

BACKGROUND

To determine whether vegetable fats cause a slower or quicker rate of gastric emptying (GE) than animal fats, we evaluated the effect of animal butter and vegetable soybean oil on solid-phase GE in patients with functional dyspepsia.

METHODS

Twenty-seven patients with functional dyspepsia were enrolled in this study. Radionuclide-labeled solid meals were used to evaluate GE. A study meal was composed of 206.8 kcal to 9.2 g protein, 45 g carbohydrate, and 10 g fat (formula 1, with animal butter: 26.2% saturated palmitic acid, 29.1% unsaturated oleic acid, 3.5% linoleic acid, and 0.5% linolenic acid; formula 2, with vegetable soybean oil: 11.0% saturated palmitic acid, 23.4% unsaturated oleic acid, 53.7% linoleic acid, and 7.8% linolenic acid). Each patient received formulas 1 and 2 as study meals on separate days. GE was represented by the gastric retention ratio of the study meal at 90 min (RR90): RR90 = residual radioactivity within the region of interest (ROI) covering the entire stomach at 90 min divided by the initial radioactivity within the ROI at 0 min.

RESULTS

The RR90 was 0.648 +/- 0.156 for formula 1 and 0.600 +/- 0.131 for formula 2. There was no significant difference for the RR99 between formulas 1 and 2 (paired Student's t test, p > 0.05). Of the 27 patients, 12 (44.4%) demonstrated an increased RR99 from formula 1 to formula 2, and the RR90 of remaining 15 (55.6%) patient decreased. In addition, neither the patients with increased RR90 nor those with decreased RR90 showed a difference of symptoms between the two study meals.

CONCLUSION

Our data suggest that there is no difference between these two types of fat on gastric emptying.

Effects of evodiamine on the secretion of testosterone in rat testicular interstitial cells

Evodiamine, a bioactive component isolated from the Chinese medicine Wu-chu-yu, exhibits vasodilative and antianoxic action. Although evodiamine indeed has many biological effects, its effects on the endocrine system are not clear. The present study explored the effects of evodiamine on testosterone secretion in vitro. Rat collagenase-dispersed testicular interstitial cells (TICs) were incubated with evodiamine (0 to 10(-4) mol/L) in the presence or absence of human chorionic gonadotropin (hCG), forskolin, 8-bromo-adenosine 3':5'-cyclic monophosphate (8-Br-cAMP), or steroidogenic precursors (including 25-hydroxycholesterol, pregnenolone, progesterone, 17alpha-hydroxyprogesterone, and androstenedione) at 34 degrees C for 1 hour. The testosterone concentration in the media samples was measured by radioimmunoassay. Evodiamine 10(-4) mol/L was effective to reduce both basal and hCG-stimulated testosterone secretion in rat TICs after 1, 2, or 4 hours of incubation. The stimulatory effect of forskolin on testosterone release in TICs was prevented by administration of evodiamine. Evodiamine 10(-4) mol/L also decreased 8-Br-cAMP- and androstenedione-stimulated testosterone secretion. These results suggest that evodiamine reduces testosterone secretion in rat TICs via a mechanism involving reduced activity of cAMP-related pathways and 17beta-hydroxysteroid dehydrogenase (17beta-HSD).

A potential complication of laparoscopy--the surgeon's herniated cervical disk

Almost all operations that were traditionally performed by open laparotomy operations can be done laparoscopically; however, surgeons may experience several negative health effects. A 37-year-old gynecologic laparoscopist had a herniated intervertebral disk at C5-6 level. Due to a negative trauma history, a possible explanation may be the nonergonomic posture that he held while performing laparoscopic surgery for many hours. To reduce the risk of this complication, we recommend that surgeons' spatial orientation and hand-eye coordination for laparoscopy be improved by sequential phases of training.

Comparison of various rhenium-188-labeled diphosphonates for the treatment of bone metastases

In the past, many diphosphonates were introduced as bone scan radiopharmaceuticals. In addition, diphosphonates have been labeled with beta-emitted isotopes and developed into useful therapeutic drugs for bone metastases. However, it is not clear which diphosphonate is the best choice when labeling with Re-188. In this study, we labeled methylene diphosphonate (MDP), hydroxyethylidene diphosphonate (HEDP), and hydroxymethane diphosphonate (HDP) with Re-188. Each radiopharmaceutical was further evaluated in two conditions (with and without carrier). Twenty-four rabbits were used (four in each group) for the analysis of the biodistributions and bone uptakes of these radiopharmaceuticals to assess their potential for clinical applicability. Four hours after intravenous injection of approximately 37 MBq (1 mCi) Re-188-labeled diphosphonate preparations, whole body scans were performed using a large-field gamma camera equipped with a high resolution collimator. Bone-to-soft tissue ratios (B/S ratio) were calculated using a computer program. Our data showed that Re-188 HEDP with carrier (10(-4) M carrier) could accumulate in the skeletal system whereas very little absorption by bone was observed in the rabbits that were injected with carrier-free Re-188 HEDP. In addition, no significant bone uptake was demonstrated for Re-188 MDP or Re-188 HDP, with or without carrier. The B/S ratio was 25.06 in the Re-188 HEDP with carrier group but less than 3 in the other groups. In conclusion, HEDP is the best choice among these three bone-seeking drugs when labeled with Re-188. But, it is necessary to add carrier when preparing Re-188 HEDP for the treatment of bone metastases.

Rhenium-188-Labeled DTPA: a new radiopharmaceutical for intravascular radiation therapy

Balloon angioplasty is a standard treatment for artherosclerotic coronary artery disease. However, its clinical value is reduced by a high restenosis rate. A new concept in preventing restenosis is the use of a liquid-filled balloon containing a beta-emitting radioisotope. In this study, we performed biodistribution studies of Re-188 perrhenate and Re-188 diethylenetriaminopentaacetate (DTPA) to assess the resulting organ dose values in the event of balloon rupture if these agents are used for the clinical inhibition of restenosis after percutaneous transluminal coronary angioplasty (PTCA). After injecting Re-188 preparations intravenously, rats were killed at 10 min, 30 min, 60 min, 2 h, and 6 h (n = 5 per group). Tissue concentrations were calculated and expressed as percent injected dose per gram or per milliliter (%ID/g or %ID/mL). In addition, urine excretion and thyroid gland uptake were evaluated in rats (n = 5 per group) with a gamma camera after administration of 37 MBq (1 mCi) of each agent. Our data showed that both agents were excreted primarily via urine. However, the excretion of Re-188 DTPA was much faster than that of Re-188 perrhenate via the urinary system. The biodistribution data revealed that radioactivity levels in the stomach and the thyroid gland were high in the perrhenate group but low in the Re-188 DTPA group. The concentration levels in other tissues including lung, liver, testis, muscle, and blood were low throughout this study for both agents. The thyroid radiation value in the Re-188 perrhenate group was 0.163 mGy/MBq, which was much higher than that of the Re-188 DTPA group (0.0167 mGy/MBq). The stomach radiation value was as high as 0.127 mGy/MBq for Re-188 perrhenate, compared with 0.013 mGy/MBq for Re-188 DTPA. In conclusion, in the event of balloon rupture, the release of Re-188 DTPA results in lower radiation doses than Re-188 perrhenate, especially to the thyroid gland and the stomach. Our data suggest that Re-188 DTPA is a useful radiopharmaceutical for endovascular irradiation.

Cytokeratin fragment 19 (CYFRA 21-1) in healthy smokers

Two hundred and ninety-three normal female non-smokers, 268 normal male non-smokers, and 224 normal male smokers were included in our comparative study to determine possible effect of smoking on the serum levels of cytokeratin fragment 19 (CYFRA 21-1). Immunoradiometric assay (IRMA) was used, and the results revealed that the mean +/- SD CYFRA 21-1 levels in the 293 normal female non-smokers, 268 normal male non-smokers, and 224 normal male smokers were 1.28 +/- 0.82, 1.38 +/- 0.74, and 1.47 +/- 0.62 ng/ml, respectively. There is no significantly statistical difference in the CYFRA 21-1 level among the three groups. In conclusion, we suggest that smoking has no effect on the serum levels of CYFRA 21-1.

Inhibition of aldosterone production by testosterone in male rats

In vivo and in vitro experiments were designed to assess the effect of testosterone on aldosterone secretion in male rats. Orchidectomized rats were injected subcutaneously with oil or testosterone propionate ([TP] 2 mg/kg) for 7 days. Intact rats were injected with oil only. The results indicate that the plasma aldosterone level was higher in orchidectomized versus intact and TP-replaced rats. In the in vitro study, testosterone caused a marked decrease of aldosterone secretion by zona glomerulosa (ZG) cells, but failed to alter the accumulation of intracellular adenosine 3',5'-cyclic monophosphate (cAMP). Testosterone significantly decreased the corticotropin (ACTH)-stimulated production of aldosterone and accumulation of cAMP in rat ZG cells. The conversion of corticosterone to aldosterone and of 25-OH-cholesterol to pregnenolone, as well as angiotensin II (ANG II)-stimulated production of aldosterone, were decreased by testosterone. These results suggest that testosterone inhibits the basal and ANG II- and ACTH-stimulated release of aldosterone, via inhibition of aldosterone synthase activity and cytochrome P-450 side-chain cleavage (P450scc) activity, and ACTH-stimulated cAMP accumulation in rat ZG cells.

Inhibition of salmon calcitonin on secretion of progesterone and GnRH-stimulated pituitary luteinizing hormone

The effects of salmon calcitonin (sCT) on the production of progesterone and secretion of luteinizing hormone (LH) were examined in female rats. Diestrous rats were intravenously injected with saline, sCT, human chorionic gonadotropin (hCG), or hCG plus sCT. Ovariectomized (Ovx) rats were injected with saline or sCT. In the in vitro experiments, granulosa cells and anterior pituitary glands (APs) were incubated with the tested drugs. Plasma LH levels of Ovx rats were reduced by sCT injection. Administration of sCT decreased the basal and hCG-stimulated progesterone release in vivo and in vitro. 8-Bromo-cAMP dose dependently increased progesterone production but did not alter the inhibitory effect of sCT. H-89 did not potentiate the inhibitory effect of sCT. Higher doses of 25-hydroxycholesterol and pregnenolone stimulated progesterone production and diminished the inhibitory effects of sCT. sCT did not decrease basal release of LH by APs, but pretreatment of sCT decreased gonadotropin-releasing hormone (GnRH)-stimulated LH secretion. These results suggested that sCT inhibits progesterone production in rats by preventing the stimulatory effect of GnRH on LH release in rat APs and acting directly on ovarian granulosa cells to decrease the activities of post-cAMP pathway and steroidogenic enzymes.

Regulation of testosterone secretion by prolactin in male rats

The goal of this study was to characterize the mechanism by which hyperprolactinemia alters testosterone production in rat testicular interstitial cells (TICs). Hyperprolactinemia was induced by grafting 2 anterior pituitary (AP) glands under the subcapsular space of the kidney in experimental rats. Control rats were grafted with brain cortex (CX). Six weeks post-grafting, rats were challenged with human chorionic gonadotropin (hCG) then, the changes in either plasma testosterone or luteinizing hormone was measured. Additionally, TICs were isolated and challenged in vitro with hCG or prolactin, and the testosterone release measured by radioimmunoassay. Further investigation in signal transduction as intracellular 3':5' cyclic adenosine monophosphate (cAMP) production was observed under a regulation of forskolin or SQ22536. After the challenge of hCG or GnRH, the AP-grafted rats showed a suppressed response in testosterone release as compared to those in the CX-grafted group. The in vitro data from the AP-grafted rats compared to the CX-grafted animals showed a diminished response in testosterone release upon hCG stimulation. Administration of forskolin or SQ22536 disclosed dysfunction of adenylate cyclase in TICs from the AP-grafted rats. When 8-Br-cAMP was incubated with TICs, the testosterone production was lower in the AP-grafted compared to the CX-grafted group. These results suggest that in addition to adenylate cyclase dysfunction, inefficiency of post-cAMP pathways are also involved in the hypogonadism elicited by hyperprolactinemia in rats.

Gastric emptying rate assessment based on the proportion of intra-abdominal radioactivity in the stomach

Using scintigraphic techniques, the rate of gastric emptying is calculated by quantifying the absolute radioactivity within a gastric region of interest (intragastric method) with the time of meal completion considered 100% retention. However, this technique has significant limitations arising from subject movement and radionuclide gamma-ray attenuation, which may render curve fitting difficult, particularly in patients with gastroparesis. In an attempt to minimize these limitations, we have expressed the intragastric content as a percentage of the total abdominal radioactivity (abdominal method) and compared these two methods.

METHODS

Forty-five subjects in a sitting position consumed a meal consisting of two fried eggs labeled with 99mTc, two slices of toast and 300 mL 5% glucose water (412 kcal). Data were acquired at a rate of one frame every 5 min from the left anterior oblique view. Using the two methods, the intragastric retention ratios at 30, 60, 90, 120 and 240 min and the 50% emptying time (T50) were obtained from both observation and calculation by power exponential fit. R2, representing goodness of fit of the nonlinear curve fitting, was calculated.

RESULTS

There were no differences in the calculated values of T50 between the two methods. Quantitative estimates of T50 by extrapolation of a power exponential fit were feasible in 42 of the 45 subjects when the abdominal method was used, compared with only 29 of the 45 subjects when the intragastric method was used. In the 23 subjects with delayed emptying, quantitative estimates of T50 were feasible in 20 subjects when the abdominal method was used, compared with 7 subjects when the intragastric method was used. Using the abdominal method as opposed to the intragastric method also significantly improved R2. The difference between observed values and estimated values of T50 and intragastric retention ratios at 30, 90 and 120 min was smaller using the abdominal method.

CONCLUSION

Scintigraphic measurement of gastric emptying calculated using the proportion of the abdominal radioactivity in the stomach offers substantial advantages over conventional methods, particularly in patients with gastroparesis.

Effects of thyroid hormones on the release of calcitonin gene-related peptide (CGRP) by rat prostate glands in vitro

It has been well known that calcitonin (CT) and calcitonin gene-related peptide (CGRP) are derived from the CT/CGRP gene which is localized in chromosome 11. CGRP is a 37-amino acid neuropeptide expressed predominantly in the nervous system and is one of the most potent endogenous vasodilatory peptides that have been found. Only few reports described the distribution of CGRP in reproductive organs. Moreover, the hormonal regulation of CGRP secretion is still not clear. The present study was designed to examine the presence of CGRP in rat prostates and the direct effect of thyroxine (T4) on the release of CGRP by rat prostate glands in vitro. Male rats were thyroidectomized (Tx) or sham Tx for two weeks before decapitation. The ventral prostate glands were either extracted by phosphate buffer saline or bisected and preincubated with Locke's solution containing 10 mM glucose, 0.03% bacitracin, and 0.05% Hepes at 37 degrees C for 90 min. The hemi-prostate tissues were then incubated with Locke's medium containing T4 (0 to approximately 10(-7) M) for 1 hr. After incubation, the medium was collected, and the prostate tissues were weighed. The concentration of CGRP in both medium and prostate tissue extracts were measured by a specific radioimmunoassay (RIA) developed in our laboratory. Incubation of T4 at 10(-9) M was effective to increase the release of CGRP in rat prostate glands. Incubation of rat prostate glands with T4 at 10(-7) M resulted in a maximal release of CGRP (270% of the basal). These results suggest that thyroid hormones increase CGRP release by acting directly on rat prostate glands.

Regulation of thyroid hormones on the production of testosterone in rats

The effects of a thyroidectomy and thyroxine (T4) replacement on the spontaneous and human chorionic gonadotropin (hCG)-stimulated secretion of testosterone and the production of adenosine 3',5'-cyclic monophosphate (cAMP) in rat testes were studied. Thyroidectomy decreased the basal levels of plasma luteinizing hormone (LH) and testosterone, which delayed the maximal response of testosterone to gonadotropin-releasing hormone (GnRH) and hCG in male rats. T4 replacement in thyroparathyroidectomized (Tx) rats restored the concentrations of plasma LH and testosterone to euthyroid levels. Thyroidectomy decreased the basal release of hypothalamic GnRH, pituitary LH, and testicular testosterone as well as the LH response to GnRH and testosterone response to hCG in vitro. T4 replacement in Tx rats restored the in vitro release of GnRH, GnRH-stimulated LH release as well as hCG-stimulated testosterone release. Administration of T4 in vitro restored the release of testosterone by rat testicular interstitial cells (TICs). The increase of testosterone release in response to forskolin and androstenedione was less in TICs from Tx rats than in that from sham Tx rats. Administration of nifedipine in vitro resulted in a decrease of testosterone release by TICs from sham Tx but not from Tx rats. The basal level of cAMP in TICs was decreased by thyroidectomy. The increased accumulation of cAMP in TICs following administration of forskolin was eliminated in Tx rats. T4 replacement in Tx restored the testosterone response to forskolin. But the testosterone response to androstenedione and the cAMP response to forskolin in TICs was not restored by T4 in Tx rats. These results suggest that the inhibitory effect of a thyroidectomy on the production of testosterone in rat TICs is in part due to: 1) the decreased basal secretion of pituitary LH and its response to GnRH; 2) the decreased response of TICs to gonadotropin; and 3) the diminished production of cAMP, influx of calcium, and activity of 17beta-HSD. T4 may enhance testosterone production by acting directly at the testicular interstitial cells of Tx rats.

Direct effects of prolactin on corticosterone release by zona fasciculata-reticularis cells from male rats

The role of prolactin (PRL) in the male is not fully defined. The aim of this study was to investigate the function and mechanism of PRL on the production of corticosterone by zona fasciculata-reticularis (ZFR) cells in vitro. The ZFR cells were obtained from male rats under normal, hyperprolactinemic, or hypoprolactinemic situation. PRL stimulated the corticosterone release in a dose-dependent pattern in the ZFR cells from normal male rats. The cellular adenosine 3'-5'-cyclic monophosphate (cAMP) concentration positively correlated with PRL concentration in the presence of forskolin or 3-isobutyl-1-methylxanthine (IBMX). PRL enhanced the stimulatory effects of cAMP mimetic reagents, i.e., forskolin, 8-bromo-adenosine 3',5'-cyclic monophosphate (8-Br-cAMP), and IBMX on the release of corticosterone. The adenylate cyclase inhibitor (SQ22536) inhibited the corticosterone release in spite of presence of PRL. Nifedipine (L-type calcium channel blocker) did not inhibit corticosterone release. The hyperprolactinemic condition was actualized by transplantation of donor rat anterior pituitary glands (APs) under kidney capsule. By comparison with the cerebral cortex (CX)-grafted group, AP-graft resulted in an increased release of corticosterone, 3beta-hydroxysteriod dehydrogenase (HSD) activity and cAMP production by ZFR cells. Acute hypoprolactinemic status was induced by bromocriptine for 2 days. The results showed the productions of corticosterone were lower in hypoprolactinemic group than in control group, which were persistent along with different ACTH concentrations. These results suggest that PRL increase the release of corticosterone by ZFR cells via cAMP cascades and 3beta-HSD activity.

Effects of estradiol on aldosterone secretion in ovariectomized rats

The effects and action mechanisms of estradiol on aldosterone secretion in female rats were studied. Replacement of estradiol benzoate (EB) increased the levels of plasma estradiol and aldosterone in ovariectomized (Ovx) rats. The aldosterone release from zona glomerulosa (ZG) cells was higher in EB-treated rats than in oil-treated animals. EB treatment potentiated the responses of aldosterone release to adrenocorticotropic hormone (ACTH), forskolin (FSK), and 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP). Administration of EB in vivo did not alter cAMP production in response to ACTH or FSK. Although angiotensin II (Ang II) increased aldosterone secretion by rat ZG cells, the stimulatory effect of Ang II on the release of aldosterone was not altered by EB treatment. The conversions of [3H]-deoxycorticosterone to [3H]-corticosterone and [3H]-corticosterone to [3H]-aldosterone in EB-treated groups were greater than those in the oil-treated group. These results suggest that estradiol increases aldosterone secretion in part through the mechanisms involving the activation of the post-cAMP pathway, 11beta-hydroxylase and aldosterone synthase activity.

Effects of hyperprolactinemia on calcitonin secretion in male rats

The role of prolactin (PRL) in calcitonin (CT) release by the thyroid C cell in male rats was studied. Anterior pituitary (AP)-grafted male rats were characterized by hyperprolactinemia. Brain cortex (CX)-grafted male rats were used as control animals. AP- and CX-grafted rats were infused intravenously with CaCl2 and bled from the jugular catheter at 0, 30, 60, and 120 minutes following the CaCl2 challenge. Rat thyroid gland was incubated with or without 3-isobutyl-1-methylxanthine (IBMX) at 37 degrees C for 30 minutes. Thyroid C cells were incubated in culture medium at 37 degrees C for 60 minutes. Cyclic adenosine 3',5'-monophosphate (cAMP) in rat thyroid tissues following incubation with IBMX was extracted by 65% ethanol. AP-grafted rats had higher plasma levels of PRL and CT compared with CX-grafted rats. Both the release of CT and accumulation of cAMP in thyroid glands were higher in AP-grafted versus CX-grafted rats. Direct administration of ovine PRL (oPRL) on the thyroid glands did not increase CT secretion in vitro. Thyroid C cells of AP-grafted rats secreted more CT compared with CX-grafted rat cells. These results suggest that hyperprolactinemia increases the release of CT by thyroid C cells in rats through a cAMP-dependent pathway caused by an indirect effect of PRL.