The effect of lighting conditions on plasma levels of gonadotropins in castrated male rats

Plasma levels of LH and FSH were measured in castrated male rats kept in a 12/12 h light/dark cycle (control lighting), continuous light or continuous darkness. In Experiment I, the animals were kept in the three illumination conditions for 5 weeks. They were then decapitated for blood collection. In Experiment II, the blood samples were collected daily via permanently implanted aortic cannulae after 7 days of adaptation to the experimental lighting condition. In both experiments, the plasma levels of LH and FSH were higher in the rats kept in continuous light than in those kept in control conditions. After exposure to darkness for 5 weeks, the gonadotropin levels did not differ from the control values. In Experiment II, the levels of FSH were lower in darkness than in the control lighting, but the levels of LH did not change.     

Ghrelin effects on gonadotropin secretion in male and female rats

Ghrelin is a 28-amino acid peptide primarily involved in the control of food intake and growth hormone secretion. The present experiments were carried out to analyze the potential involvement of ghrelin in the control of gonadotropin secretion. Prepubertal intact and gonadectomized female and male rats, cyclic rats in diestrus, lactating rats and aged female rats were i.c.v. injected with ghrelin (3 nmol/rat) and blood samples were obtained by decapitation 15 min later. In addition, we analyzed the effects of ghrelin on in vitro basal and luteinizing hormone-releasing hormone (LHRH)-stimulated gonadotropin secretion. Our present results indicate that ghrelin inhibited luteinizing hormone (LH) secretion in vivo in prepubertal males as well as gonadectomized males and females, whereas follicle-stimulating hormone (FSH) remained unaffected. In vitro, ghrelin stimulated the secretion of both gonadotropins, and differentially modulated the response to LHRH; the LH response was inhibited, while the FSH response was enhanced. Overall, our current data open up the possibility that ghrelin may be involved in the control of LH secretion, and in the dissociation of both gonadotropins that takes place in many physiological, pathological and experimental situations.     

Episodic secretion of hormones and the diagnostic value of single blood estimates. I. LH, FSH, prolactin

The episode fluctuation of serum LH, FSH and prolactin levels in peripheral blood was studied to determine the reliability of single estimates of the average blood level. Radioimmunoassay of the hormones was performed in serum withdrawn every 10 min between 8 and 12 h a.m. from 8 healthy women in various periods of the menstrual cycle. The rate of fluctuation of the hormone levels was characterized by the within-person coefficient of variation of single estimates, which averaged 30.3, 15.1 and 19.2% for LH, FSH and prolactin, respectively. Due to a pronounced fluctuation of gonadotropin levels, analysis of several serum samples is recommended to approach the actual mean hormone level.     

Effect of exogenous gonadotropins on gonadotrophs of the rat pituitary gland

In the human in vitro fertilization (IVF) program a variety of superovulation regimens have been employed to promote follicular stimulation and the recruitment of supernumerary oocytes. This therapy, however, disturbs serum concentrations of estradiol and progesterone and may disrupt the normal feedback systems of the hypothalamo-pituitary axis. This study examines the effects of hyperstimulation on the pituitary gonadotrophs and circulating gonadotrophins. FSH and human chorionic gonadotropin (hCG) were administered to normal cycling female Sprague-Dawley rats (n = 12) in phase with their estrous cycle. Control rats (n = 12) were injected with saline. In both the experimental and control groups, six rats were mated on the evening of proestrus and killed 12 hr later, while six animals were killed prior to mating. Blood was collected at the time of sacrifice for radioimmunoassay. The pituitary glands were removed, processed for light microscopy and serially sectioned. Immunocytochemistry for LH and FSH was carried out to determine the area occupied by these cell types. Data were statistically analyzed. Findings were correlated with circulating levels of LH, FSH, estradiol and progesterone. RIA revealed that the concentration of LH, FSH, estradiol and progesterone were significantly different with respect to hyperstimulation and mating. In addition the area occupied by LH and FSH cells was significantly different with respect to both hyperstimulation and mating. Hyperstimulation affects gonadotroph content, as well as gonadotropin and sex steroid hormone concentrations and together with other factors, may disrupt the ideal environment required for implantation.     

Ontogeny of sex differences in LH and FSH levels 48 h after castration in the rat

Serum gonadotropin levels were measured 12, 24, and 48 h after gonadectomy in male and female rats (ages, 22--60 days) to assess when during development the rate of rise of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) after castration approximates that seen in the gonadectomized adult. In females serum LH levels 48 h after ovariectomy were increased above sham levels only when the ovaries were removed prior to vaginal opening. Ovariectomy on the day of vaginal opening or at older ages resulted in no increase in LH levels by 48 h after surgery. Serum FSH levels at 24 and 48 h after ovariectomy declined with increasing age at the time of ovariectomy. In males serum LH levels at 48 h after castration increased with increasing age at the time of gonadectomy. Serum FSH levels at either 12, 24, or 48 h after orchidectomy did not change appreciably with age at the time of surgery. It is concluded that the acute pituitary secretion of gonadotropins after removal of testes in the immature male resembles that seen in the mature male early in the course of the development of sexual maturity. In contrast, the acute pituitary secretion of gonadotropins after removal of the ovaries in the immature female does not resemble that seen in the ovariectomized adult until she is mature and capable of ovulating. Thus, the observed delay in the rise of LH seen in ovariectomized adults may be a function of some aspect of the hormonal changes associated with the estrous cycle.     

Modulatory role of gamma-aminobutyric acid (GABA) in the regulation of gonadotropin secretion in patients with chronic renal failure

The role of gamma-aminobutyric acid (GABA) in the regulation of gonadotropin secretion in renal failure, was studied in 5 patients with chronic renal failure who were on maintenance dialysis. Di-n-propylacetic acid (valproic acid-VA), a GABA-transaminase inhibitor which has been shown to increase brain GABA levels, was used in the study. VA produced no significant change in the basal serum LH and FSH concentrations, or in E2 or T concentrations in the renal failure patients, or the E2 and P concentrations in normal controls, but augmented the delta LH (maximum increment above baseline) and delta FSH response to LH-RH. delta LH rose from 30.4 +/- 12.7 mIU/ml (mean +/- SD) to 41.1 +/- 16.8 mIU/ml (p less than 0.01) after VA, while delta FSH rose from 2.8 +/- 1.8 mIU/ml to 3.8 +/- 1.6 mIU/ml (p less than 0.05). The findings support a modulatory role for GABA in gonadotropin secretion in chronic renal failure.     

Action of PMSG and asialo-PMSG on rat Leydig and granulosa cells.

Highly purified pregnant mares serum gonadotropin (PMSG) was nearly as potent as ovine luteinizing hormone (LH) and human follicle stimulating hormone (hFSH) when bioassayed in vitro in systems known to respond primarily to LH or FSH. An analogue of human chorionic gonadotropin treated with neuraminidase, galactosidase, beta-N-acetylglucosaminidase, and mannosidase (hCG) inhibited the stimulatory effects of hCG, LH, and PMGS on cAMP accumulation in rat Leydig cells but did not inhibit the stimulatory effects of FSH or PMSG on cAMP accumulation in ovarian granulosa cells obtained from immature rats fed diethylstillbestrol. Thus PMSG appeared to form functional complexes with both LH and FSH receptors and may be unique among mammalian gonadotropins. Treatment of PMGS with neuraminidase increased its potency nearly tenfold in vitro apparently by increasing its affinity for both LH and FSH receptors. Although the kinetics of PMSG binding were not investigated with radiolabeled materials, indirect functional binding studies are described that suggest that hCG more rapidly forms stable hormone-receptor complexes than PMSG, asialo-PMSG, FSH, and LH when all hormones are incubated under the same conditions.     

Endocrinology: Melatonin potentiates testosterone-induced suppression of luteinizing hormone secretion in normal men

A total of 12 healthy adult men were recruited to investigatethe effect of exogenous melatonin on the sensitivity of thehypothalamo-pituitary axis to sex steroid negative feedback.The experiment consisted of a double-blind, randomized cross-overtrial during which all subjects received 100 mg oral melatoninor placebo at 1600 h for 14 days. Midway through each of thetwo treatments (day 8), 100 mg testosterone propionate i.m.(TP) was given at 0900 h. Blood samples for the measurementof luteinizing hormone (LH), follicle stimulating hormone (FSH),prolactin, testosterone and melatonin were taken at 0900 h ondays 1, 3, 5, and daily from days 8–14. An additionalblood sample was taken 8 h after the administration of testosterone.The interval between the melatonin and placebo treatment periodswas 2 months. The oral administration of melatonin caused apharmacological increase in the blood plasma concentration ofmelatonin which was maximum at 2 h and still above normal at24 h. The daily treatment thus resulted in persistently highcirculating levels of melatonin for 14 days. This treatmenthad no significant effect on the secretion of LH, FSH, prolactinor testosterone based on the first week of each study (melatonincompared with placebo). The injection of TP caused a rapid 3to 4-fold increase in the plasma concentrations of testosteronewhich was at a maximum at 8 h and had returned to baseline within4 days, with a similar pattern in both the melatonin and placeboperiods. This dose of TP caused a decrease in the plasma concentrationsof LH and FSH lasting 4 days; there was no change in the concentrationof prolactin. The steroid-induced, time-dependent reductionin the plasma concentration of LH was significantly greaterin the subjects receiving melatonin compared with placebo (analysisof variance P < 0.01); LH concentrations were suppressedto a greater extent and for one day longer during the administrationof melatonin. This effect did not reach statistical significancefor the changes in the plasma concentration of FSH. These resultsshow that the sensitivity of the hypothalamo-pituitary axisto testosterone feedback is increased by pharmacological treatmentwith melatonin, and suggest novel strategies for the developmentof hormonal contraception in men.     

PRL细胞腺瘤过度分泌对促性腺激素水平及性腺功能的影响

利用ＲＩＡ测定ＰＲＬ细胞腺瘤患者血清中ＰＲＬ，ＦＳＨ，ＬＨ，Ｔ水平，探讨ＰＲＬ细胞腺瘤过度分泌ＰＲＬ对促性原激素以及对男性性功能的影响。结果在３６６例ＰＲＬ细胞腺瘤患者中，１５９例，血清ＦＳＨ水平低于正常，１４８例，血清ＬＨ水平低于正常，８例血清ＦＳＨ水平高于正常，１０例血清ＬＨ水平高于正常。     

能量限制对化疗大鼠卵巢的形态结构与功能的保护作用

目的探讨能量限制对环磷酰胺处理大鼠卵巢的保护作用。方法将48只10周龄大鼠随机分为对照组、能量限制组、环磷酰胺组、能量限制加环磷酰胺组。观察各组动物的动情周期,实验结束时称取卵巢重量,并进行卵巢组织形态学观察及卵泡计数,测定血清雌二醇、促黄体生成素、促卵泡生成激素评估卵巢储备功能。结果经环磷酰胺处理的大鼠出现精神萎靡、体重下降、动情周期逐渐消失,卵巢体积缩小,颗粒细胞变性、坏死,各期卵泡数均明显减少,闭锁卵泡数增加（P〈0.01）。能量限制组大鼠卵巢的原始卵泡数比对照组明显增多（P〈0.01）,窦状卵泡数减少（P〈0.01）。能量限制加环磷酰胺组的原始卵泡和初级卵泡数比环磷酰胺组明显增多（P〈0.01）,且卵巢组织受损程度较单用环磷酰胺轻。环磷酰胺处理组大鼠血清雌二醇显著低于对照组和能量限制组,促黄体生成素和促卵泡生成素水平则显著高于对照组和能量限制组（P〈0.01）。结论能量限制模型可以抑制原始卵泡的的转化使其数量明显增多,并可以适度减轻化疗造成的结构与功能损伤,使卵巢保留有一定储备功能。     

Stress and local cerebral blood flow: studies on restrained and unrestrained rats

Summary The degree of stress has been compared between two protocols used for the measurement of local cerebral blood flow (LCBF) in conscious rats. The first method involved acute surgical procedures (cannulation of both femoral veins and arteries) under halothane anesthesia. It was followed by a recovery period (2–3 h) during which the rat was before LCBF measurement. The second method employed chronic cannulation of the abdominal aorta and vena cava, allowing the LCBF assays to be performed on freely moving rats. Plasma corticosterone and a glucose tolerance tests showed that the freely moving rats were less stressed than the gently restrained ones. The LCBF of the two groups were not significantly different except in the frontal and parietal cortex, where it was more elevated in the freely moving rats. LCBF may be sensitive to the environmental conditions in freely moving rats whereas these vascular effects may be reduced after 2–3 h of gentle restraint. The two protocols tested in this study could be considered as good methods for studying LCBF in conscious rats, although some stress remained in gently restrained rats. Freely moving rats can be used for behavioural studies providing that the time lag of the arterial samples is taken into account. Since the basal LCBF values of gently restrained rats are minimally affected by the stress inherent in the preparation, this convenient protocol could be considered as useful for numerous investigations.     

促性腺激素释放激素类似物对大鼠中缝核簇5-HT样阳性物质表达的影响

研究促性腺激素释放激素类似物 ( Gn RH-A)对大鼠中缝核簇 5 -HT样阳性物质表达的影响 ,采用酶联免疫吸附试验测定血清激素水平 ,用免疫组织化学方法和图像分析技术观察大鼠中缝核簇 5 -HT样阳性物质的表达。结果证明 :( 1) Gn RH-A组大鼠血清 17β-雌二醇 ( E2 )、LH及 FSH水平较正常对照组下降 ,差异显著 ( P<0 .0 5 ) ;与去卵巢组 ( OVX)比较 ,E2 相似 ,差异不显著 ( P>0 .0 5 ) ,但 L H、F SH较低 ( P<0 .0 5 ) ;与 Gn RH-A+E2 组比较 E2 浓度较低 ,差异显著 ( P<0 .0 5 ) ,L H、FSH相似 ( P>0 .0 5 )。( 2 ) 5 -HT样阳性物质在大鼠中缝背核 ,中缝正中核表达较多 ,Gn RH-A组大鼠中缝背核 ,中缝正中核 5 -HT样阳性细胞数及光密度值都低于正常对照组 ( P<0 .0 5 ) ,与去卵巢组相似 ( P>0 .0 5 )。 ( 3 ) Gn RH-A、17β-雌二醇联合用药后 ,大鼠中缝背核 ,中缝正中核 5 -HT样阳性细胞数及光密度值都与正常对照组相似 ,无显著差异 ( P>0 .0 5 )。结论 :Gn RH-A可改变大鼠中缝背核 ,中缝正中核 5 -HT样阳性物质表达 ,从而影响其神经元的功能 ,此点可能与其副作用类似绝经综合征有关。     

Analysis of histophysiologic responses of the rat hypophysis to androgen treatment

The concentrations of LH and FSH were measured in the blood and adenohypophyses of castrated male rats exposed to high levels of testosterone propionate for 1 to 18 weeks. In intact male and female rats, similarly treated for 1 to 5 weeks, blood levels could not be measured but pituitary hormone levels were. Histological study of the pituitary gonadotrophic cells of all groups revealed a striking correlation between their regression, in response to androgen treatment, and the decline in pituitary LH stores. No light-microscopic correlate of the marked, progressive increase in pituitary FSH concentration was detected. Thus, when the pituitary FSH:LH ratio had increased 90 fold, all gonadotrophs appeared inactive. Although these studies failed to reveal the specific cellular source(s) of FSH and LH, they did clarify several aspects of the dynamics of the pituitary secretory responses to orchidectomy and androgen treatment. In the light of this information, the suggestion is made that the greatest dichotomy between pituitary FSH and LH stores is not coincident with — and probably occurs later than — that between LH and FSH secretion. Such asynchrony between the various phases of the FSH and LH secretory responses to these treatments (castration and/or androgen administration), may explain several seeming discrepancies among earlier reports on this subject.     

Plasma catecholamines in salt-sensitive hypertensive (Dahl) rats

We examined the effects of low (0.4%) and high (8.0%) salt diets on basal and stress-induced increments in plasma levels of norepinephrine (NE) and epinephrine (EPI) in the Dahl lines of salt-sensitive (DS) and salt-resistant (DR) rats. DS rats develop sustained increases in blood pressure when maintained on a high salt diet while DR rats remain normotensive. For this study, blood samples were obtained via a chronic tail artery catheter from DS and DR rats under resting conditions or following exposure to stress. Plasma samples were later assayed for content of NE and EPI by a radioenzymatic assay. Basal plasma levels of both catecholamines were similar in DS and DR rats, irrespective of dietary salt content and mean arterial blood pressure. The mild stress of handling and transfer of rats to a different cage resulted in greater increments in plasma NE but not EPI in DS rats fed a high salt diet compared to DS rats fed a low salt diet. There was a significant effect of line and an interaction of line and diet with respect to the effects of immobilization stress on plasma catecholamines. DS rats had greater immobilization-induced increments in plasma NE and EPI compared to DR rats when both lines were fed a low salt diet. Maintenance on a diet high in salt resulted in lesser immobilization-induced increments in plasma catecholamines for DS rats and greater immobilization-induced increments in plasma catecholamines for DR rats when compared to their respective controls on a low salt diet. There was a significant effect of diet on plasma levels of both catecholamines when blood samples were obtained by decapitation. DS and DR rats that were fed a high salt diet had lower plasma levels of NE and EPI following decapitation compared to rats of the two lines that were fed a low salt diet. These findings demonstrate that dietary salt and genetic factors are important in regulating the activity and responsiveness of the sympathetic-adrenal medullary system to a variety of stressors. Our findings do not provide evidence for a critical role of the sympathetic nervous system in maintaining the diet-induced increase in the arterial blood pressure of DS rats.     

Differential effects of flurothyl- and electro-convulsive shock on sexual maturation and prolactin release in the rat

Summary The effects of single and repeated seizures on luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin secretion and on the onset of sexual maturation in rats are described. In addition, the influence of convulsions generated electrically (electroconvulsive shock, ECS) and chemically (using flurothyl) are compared. Repeated flurothyl convulsions and ECS (one daily convulsion from age 24 days) significantly delay vaginal opening in female rats. The incidence of first ovulation at maturation is reduced to 20% compared with 70–100% for untreated groups. Body and adrenal weights in immature rats are not modified by flurothyl convulsions. Repeated ECS does not influence adrenal weight although somatic growth is inhibited. In an effort to clarify the mechanism of action of convulsions on puberty onset, we examined acute changes in LH, FSH and prolactin secretion and the surge response of LH/FSH to gonadal steroid priming. A single flurothyl convulsion potently inhibits prolactin secretion. In contrast, an ECS acutely stimulates prolactin release in male and female rats. Convulsive seizures do not consistently alter tonic gonadotropin output. However, both flurothyl convulsions and ECS attenuate estradiol benzoate/progesterone-induced LH and FSH surges in ovariectomized rats though this is apparently not mediated by dopamine/prolactin since bromocriptine treatment delays sexual maturation without preventing ovulation at first estrus. Similarly, bromocriptine does not disrupt LH/FSH surges induced by gonadal steroid treatment. One component in the neural response to convulsions may be hypothalamic endogenous opiate peptides since the ability of naloxone to influence LH and prolactin secretion is potentiated by repeated ECS. On the other hand, dopamine is clearly implicated in the flurothyl-induced inhibition of prolactin secretion, since haloperidol reverses this effect.     

Gonadotropin and androgen levels in patients operated upon for cryptorchidism

53 patients previously operated upon for cryptorchidism were examined seven years (range 2-18) after the operation. We measured serum levels of sex-hormone-binding-globulin (SHBG), testosterone (T), free testosterone (free T), dihydrotestosterone (DHT), 4 androstenedione (4-AD), and dehydroepiandrosteronesulphate (DHAS), and the gonadotropin luteinizing hormone (LH) and follicular hormone stimulating (FSH). Compared to normal controls, there were decreased levels of free testosterone and DHT and increased levels of SHBG and DHAS. The FSH levels were elevated and LH values low. No relationship was found between androgen and gonadotropin levels, suggesting that the normal feed-back mechanism is malfunctioning. There were no hormonal differences between patients with previous unilateral and bilateral cryptorchidism, although SHBG levels were higher in the former. We concluded that cryptorchidism is probably due to a defect in the hypothalamic-pituitary axis and not to a primary defect in the testes.     

The human gonadotropic adenoma: pathologic diagnosis and hormonal correlations in 26 tumors

Twenty-six out of 400 surgically removed pituitary tumors were identified as gonadotropic adenomas (frequency 6.25%). Morphologic, immunocytochemical, and hormonal characteristics of the gonadotropic adenoma are described. The following morphologic characteristics may suggest the diagnosis: arrangement in cords of cells showing signs of cellular activity, secretory granules, which vary in electron density, form, and size (mean diameter 150 nm) and which are numerous in the extensions near the capillaries, and a rough endoplasmic reticulum arranged in short cisternae. However, owing to the morphofunctional variations from one adenoma to another, we consider that only immunoreactivity with gonadotropin antisera proves the diagnosis. Because the material used to generate the gonadotropin antisera was purified but not pure, for precise characterization of the immunoreactivity, absorption tests with various antigens have to be performed. FSH-LH adenomas (n = 14), FSH adenomas (n = 7), and alpha-subunit adenomas (n = 5) but no LH adenomas were identified in our series. No evident morphologic difference related to the type of immunoreactivity and to the sex was found. Almost all the tumors were large with visual signs caused by suprasellar extension. A recurrence following adenomectomy was noted with a frequency of 12%. The diagnosis of gonadotropic adenoma was considered preoperatively in six out of 26 patients only, on the basis of increased serum gonadotropin levels. Correlations between hormonal levels and pathologic data were established in 17 patients. Seven tumors were associated with high serum gonadotropin levels (FSH and LH: three patients and FSH alone: four patients). In ten cases, the serum gonadotropin levels were normal but serum alpha-subunit assay had not been performed. For the pathologist systematically testing the adenomas with many antisera, gonadotropic adenomas are not as rare as for the clinician. Immunocytochemical studies with gonadotropin antisera and serum gonadotropic determination must be performed in all tumors, especially in those pituitary adenomas that appear nonfunctional.     

L-精氨酸甲基酯对大鼠垂体-睾丸轴激素分泌的剂量影响

目的　探讨L 精氨酸甲基酯 (N nitro L argininemythelester,L NAME)剂量与血清内促性腺激素和睾酮含量的关系 ,阐明一氧化氮 (Nitricoxide,NO)对垂体 睾丸轴内分泌功能的调节作用。方法　健康成年雄性SD大鼠分为 8组 ,每组 5只 ,腹腔内给予不同剂量的L NAME(0～ 70mg/kg) ,对照组注射D NAME放射免疫法测定血清中促卵泡素 (Folliclestimulatinghormone,FSH)、促黄体素 (Luteinizinghormone ,LH)、雄激素含量 ,对所得数据用SPSS软件包进行统计学处理。结果　L NAME剂量越大 ,FSH含量越低 (r =0 947,p <0 0 1) ,LH含量也随剂量的增加而降低 (r=0 983 ,p <0 0 1) ,而雄激素浓度则随剂量的增加而增加(r=0 993 ,p <0 0 1)。 结论　L NAME剂量与促性腺激素和睾酮分泌具有高度相关性     

Mutationen der Gonadotropine und Gonadotropinrezeptoren

The gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are fundamental for reproduction. They exert their action through specific receptors located exclusively in gonadal somatic cells. Mutations of the gonadotropins and their receptors are very rare but help to elucidate the mechanism of gonadotropin action. To date, only one missense mutation of the LH β-subunit and two missense mutations and one deletion of the FSH β-subunit gene have been described. These mutations lead to loss of gonadotropin function and hypogonadism. Selective loss of FSH in men caused by mutations in the β-chain result in azoospermia. For gonadotropin receptors, about two dozen loss-of-function (inactivating) and gain-of-function (activating) mutations are known. Inactivating mutations of the LH receptor cause Leydig cell hypoplasia with various degrees of hypoandrogenization up to male pseudohermaphroditism, while in females they result in primary amenorrhea. Activating mutations of the LH receptor are responsible for familial male-limited pseudoprecocious puberty (testotoxicosis) but do not cause phenotypic alterations in females. Inactivating mutations of the FSH receptor result in primary or early secondary amenorrhea in females and reduced spermatogenesis in males. Only one activating mutation of the FSH receptor has been described so far, in a hypophysectomized man with normal spermatogenesis in the absence of gonadotropins and very low endogenous testosterone levels. In addition, several polymorphisms in both gonadotropins and gonadotropin receptor genes have been identified, and their impact on gonadal pathophysiology is currently being investigated.     

In vivo release rates of substance P in the preoptic/anterior hypothalamic area of ovariectomized and ovariectomized estrogen-primed rats: correlation with luteinizing hormone and prolactin levels

Push-pull cannulae were implanted into the preoptic/anterior hypothalamic area (POA) of ovariectomized (OVX) rats. After recovery animals were treated with estradiol (E2) or corn oil and they were perfused 3 days later. Substance P (SP) concentrations were measured in 15 min perfusate fractions, blood samples were taken at similar intervals. SP concentration in POA perfusates were readily measurable. Following estrogen priming SP release increased significantly each afternoon prior to the estrogen induced prolactin and luteinizing hormone (LH) surges. No such increase of SP release was observed in OVX rats with constant LH and prolactin levels throughout the day. Mean SP rates in OVX rats were significantly higher in comparison to OVX estrogen-primed rats. These results indicate that SP may be involved in the feedback mechanisms of estrogen on prolactin and LH release. Authenticity of SP in POA perfusates was made probable by high-performance liquid chromatography (HPLC) where synthetic SP eluted at the same retention time as the signal measured in push-pull perfusates.