Impact of thyroid autoimmunity in euthyroid women on live birth rate after IUI.

Study question: Does thyroid autoimmunity (TAI) predict live birth rate in euthyroid women after one treatment cycle in IUI patients? Summary answer: TAI as such does not influence pregnancy outcome after IUI treatment. What is known already: The role of TAI on pregnancy outcome in the case of IVF/ICSI is largely debated in the literature. This is the first study to address this issue in the case of IUI. Study design, size, duration: This was a retrospective cohort study. A two-armed study design was performed: patients anti-thyroid peroxidase (TPO)+ and patients anti-TPO-. All patients who started their first IUI cycle in our fertility center between 1 January 2010 and 31 December 2014 were included. After exclusion of those patients with or being treated for thyroid dysfunction, 3143 patients were finally included in the study. Participants/materials, setting, methods: After approval by the institutional review board we retrospectively included all patients who started their first IUI cycle in our center between 1 January 2010 and 31 December 2014 with follow-up of outcome until 31 December 2015. Patients with clinical thyroid dysfunction were excluded (thyroid-stimulating hormone (TSH) <0.01 mIU/l; TSH >5 mIU/l) as were patients under treatment with levothyroxine or anti-thyroid drugs. These patients were then divided into two main groups: patients anti-TPO+ and patients anti-TPO- (= control group). Live birth delivery after 25 weeks of gestation was taken as the primary endpoint of our study. As a secondary endpoint, we evaluated differences in live birth delivery after IUI according to different upper limits of preconception TSH thresholds (<2.5 and <5.0 mIU/l). Furthermore, the influence of thyroid function (TSH, free thyroxine (fT4)), anti-TPO status, age, smoking, BMI, parity, ovarian reserve (anti-mullerian hormone (AMH) and FSH), IUI indication and IUI stimulation on live birth rate was analyzed. Main results and the role of chance: Between-group comparison did not show any significant difference between the anti-TPO+ and anti-TPO- group with respect to live birth delivery-, pregnancy- or miscarriage rate with odds ratio at 1.04 (95% CI: 0.63; 1.69), 0.98 (95% CI: 0.62; 1.55) and 0.74 (95% CI: 0.23; 2.39), respectively. In addition, there were no significant differences in live birth delivery-, pregnancy- or miscarriage rate when comparing subgroups according to TSH level (TSH ≥2.5 mIU/l vs. TSH <2.5 mIU/l) with an odds ratio at 1.05 (95% CI: 0.76; 1.47), 1.04 (95% CI: 0.77; 1.41) and  0.95 (95% CI: 0.47; 1.94), respectively. Limitations, reasons for caution: This study was powered for the primary aim, live birth rate. The limitations of this study are the absence of region-specific reference ranges for thyroid hormones and the absence of follow-up of TSH values during ART and subsequent pregnancy. Moreover, there was a time difference of 5 months between thyroid assessment and the start of stimulation. The area where the study was conducted corresponds to a mild iodine deficient area and data should be translated with caution to areas with different iodine backgrounds. Wider implications of the findings: Our findings indicate comparable pregnancy-, abortion- and delivery rates in women with and without TAI undergoing IUI. Moreover, we were unable to confirm a negative effect of TSH level above 2.5 mIU/l on live birth delivery rate. We therefore believe that advocating Levothyroxine treatment at TSH levels between 2.5 and 4 mIU/l needs to be considered with caution and requires further analysis in a prospective cohort study. Study funding/competing interest(s): No external funding was used for this study. No conflicts of interest are declared.

[Place of fibrates for the treatment of patients with atherogenic dyslipidemia]. / Place des fibrates dans le traitement de patients avec une dyslipidémie athérogène.

The demography of dyslipidemia has changed towards a more complex atherogenic dyslipidemia involving increased levels of LDL cholesterol, in particular highly atherogenic small dense particles, hypertriglyceridemia and low HDL cholesterol, together with increased levels of markers of inflammation, thrombogenesis and endothelial dysfunction. Statins were shown to significantly lower cardiovascular morbidity and mortality, but treated patients are still left with a high residual risk, in particular for those with metabolic syndrome, type 2 diabetes, or low HDL cholesterol levels. Fibrates have been shown to reduce plasma triglycerides and increase HDL cholesterol, while improving inflammation, thrombogenesis and endothelial dysfunction. Clinical trials with fibrates have demonstrated their potential to reduce cardiovascular morbidity and mortality too, often through other mechanisms than those of statins. Combination trials of statins with fibrates have shown a more complete improvement of lipid profile and risk markers than each class separately. In contrast with gemfibrozil, fenofibrate does not interact significantly with the pharmacokinetics of statins, and its combination with statins has been shown to have a low risk of muscular side-effects or liver toxicity. The ACCORD outcome trial is exploring possible benefits of the combination of fenofibrate with statins on morbidity and mortality of patients with type 2 diabetes.

Men with atherosclerotic stenosis of the carotid artery have lower testosterone levels compared with controls.

AIM: There is evidence to suggest an inverse association between serum levels of testosterone and coronary heart disease. The aim of this study was to compare endogenous sex hormone levels of men with severe internal carotid artery (ICA) atherosclerosis with age-matched controls. METHODS: Metabolic parameters and sex hormones were measured or calculated in 124 male patients undergoing carotid endarterectomy for high grade ICA stenosis and in 124 age-matched male controls. The presence or absence of atherosclerotic stenosis of ICA was determined by high resolution B-mode ultrasound. RESULTS: The cases had statistically significant lower levels of total testosterone (TT) (medians: 3.8 microg/L versus 4.3 microg/L, P=0.005) and sex hormone binding globulin (SHBG) (means: 39.8+/-17.2 versus 54.3+/-34.3 nmol/L, P<0.001) compared to controls. Multivariate linear regression analysis, adjusted for all clinical and physiologic parameters, showed a significant inverse association between ICA stenosis and TT (b=-0.158, P=0.013) and SHBG (beta=-0.259, P<0.001). CONCLUSION: This study provides evidence of a positive association between low serum androgen levels and severe ICA atherosclerosis in men. It suggests that higher, but physiological, levels of androgens could have a protective role in the development of atherosclerosis.

Central diabetes insipidus: beware of Langerhans cell histiocytosis!

Langerhans cell histiocytosis (LCH) is a rare disorder, characterised by a monoclonal proliferation of aberrant histiocytes that accumulate in and infiltrate into different organs. When the hypothalamic-pituitary axis is involved, central diabetes insipidus (CDI) can be its first manifestation. Three cases of LCH with central diabetes insipidus were retrospectively analyzed: Case 1 is a 41-year old female presenting with polyuria and polydipsia. Diabetes insipidus was diagnosed and treated with desmopressin. MRI pituitary showed hypophysitis. Subsequently, she developed bone lesions and a biopsy demonstrated LCH. Case 2 is a 51-year old female presenting in 2009 with polyuria and polydipsia. Diabetes insipidus was diagnosed and treated with desmopressin. MRI pituitary revealed hypophysitis. LCH was suspected because of known pulmonary histiocytosis. Coexisting bone lesions were biopsied and confirmed LCH. Case 3 is a 44-year old female presenting with diabetes insipidus. She was treated with desmopressin as well. MRI of the pituitary gland showed impressive thickening of the infundibulum. A few months later, she developed skin lesions and a biopsy revealed LCH. Conclusively, LCH is a rare, elusive and probably underdiagnosed disease with a broad disease spectrum. Due to infiltration of the hypothalamic-pituitary axis, CDI can be the first manifestation, even before LCH is diagnosed. Therefore, LCH should be considered in the diagnostic workup of CDI.

A new mutation in the calcium-sensing receptor gene causing hypocalcaemia: case report of a father and two sons.

BACKGROUND: Regulation of calcium is mediated by parathyroid hormone (PTH) and 1.25-dihydroxyvitamine D3. The calcium-sensing receptor (CaSR) regulates PTH release by a negative feedback system. Gain-of-function mutations in the CaSR gene reset the calcium-PTH axis, leading to hypocalcaemia. PATIENTS AND METHODS: We analysed a family with hypocalcaemia. The proband was a 47-year-old man (index, patient I1), who presented with paraesthesias in both limbs. He has two sons (patient II1 a nd I I2). The probands' lab results showed: serum calcium of 1.95 mmol/l, albumin 41 g/l, phosphate 0.81 mmol/l and PTH 6.6 ng/l (normal 15-65 ng/l). Based on this analysis, we suspected a hereditary form of hypocalcaemia and performed genetic testing by polymerase chain reaction and Sanger sequencing of the coding regions and intron boundaries of the CaSR gene. Genetic analysis revealed a new heterozygous mutation: c.2195A>G, p.(Asn732Ser) in exon 7. The lab results of patient II1 showed: serum calcium of 1.93 mmol/l, phosphate 1.31 mmol/l, albumin 41 g/l, and PTH 24.3 ng/l. His genotype revealed the same activating mutation and, like his father, he also lost his scalp hair at an early adolescent age. Patient II2 is asymptomatic, and has neither biochemical abnormalities, nor the familial CaSR gene mutation. He still has all his scalp hair. CONCLUSIONS: 1) The c.2195A>G, p.(Asn732Ser) mutation in exon 7 of the CaSR gene leads to hypocalcaemia, and has not been reported before in the medical literature. 2) Possibly, this mutation is linked to premature baldness.

Is systematic screening for thyroid disorders indicated in subfertile men?

CONTEXT: Data on the prevalence of thyroid disorders in male subfertility remain scarce. OBJECTIVE: To investigate the prevalence of thyroid dysfunction and thyroid autoimmunity in men with normal and abnormal semen characteristics. SETTING: Tertiary referral center for reproductive medicine of the University Hospital AZ-VUB, Brussels, Belgium. PATIENTS AND DESIGN: Two hundred and ninety-two men were stratified according to the presence of normal (group 1; n = 39) or abnormal (group 2; n = 253) semen characteristics. Thyroid function was assessed by serum thyrotropin (TSH) and free thyroxine (FT4), and thyroid peroxidase antibodies (TPO-Ab) for thyroid autoimmunity (TAI or TPO-Ab > 34 kU/l); both were correlated with semen characteristics. MAIN OUTCOME MEASURES: Semen characteristics were determined by World Health Organisation criteria (rapid + slow motility > or = 50% and concentration > or = 20 x 10(6)) and Kruger criteria (morphology > or = 14% normal cells). RESULTS: In group 1, the mean (+/- s.d.) age was 33 +/- 4 years; serum TSH was 1.6 (0.3-29.6) mU/l (median (range)) and FT4 was 12.2 (8.8-15.6) ng/l. In group 2, the mean age was 33 +/- 5 years, serum TSH was 1.3 (0.3-5.2) mU/l and FT4 was 12.5 (8.4-17.5) ng/l; (compared with group 1 P = 0.008 for TSH and P = 0.037 for FT4). In both groups, one patient had increased TSH (2.6% and 0.4%; P = not significant (ns)). In group 1, one patient had TAI and in group 2 twelve patients had TAI (2.6% compared with 4.7%; P = ns). FT4 was an independent determinant for semen characteristics. CONCLUSIONS: The prevalence of thyroid dysfunction and autoimmunity is comparable between men with normal and abnormal semen characteristics. On the basis of these data, we do not advise systematic screening for thyroid disorders in subfertile men consulting a tertiary referral center for reproductive medicine.

Thyroid autoimmunity and female infertility.

In infertile women, the prevalence of thyroid autoimmunity (TAI) is significantly higher compared to that in parous age-matched women. This is especially the case in women with endometriosis and the polycystic ovarian syndrome. TAI does not interfere with normal fetal implantation and comparable pregnancy rates have been observed after assisted reproductive technology (ART) in women with and without TAI. During the first trimester however, pregnant women with TAI carry a significantly increased risk for a miscarriage compared to women without TAI, even when euthyroidism was present before pregnancy. It has further been demonstrated that controlled ovarian hyperstimulation (COH) in preparation for ART has a significant impact on thyroid function, particularly in women with TAI. It is therefore advised to measure thyroid function and detect TAI in infertile women, before ART, and to follow-up these parameters after COH and during pregnancy when TAI was initially present. Women with thyroid dysfunction before or at early gestation stages should be treated with 1-thyroxine to avoid assisted pregnancy or further pregnancy complications. Whether thyroid hormones should be given prior to or during pregnancy in euthyroid women with TAI remains controversial and needs further investigation.

Glomerular filtration rate in patients with Cushing's disease: a matched case-control study.

BACKGROUND: Patients with Cushing's disease have a high prevalence of atherosclerosis and maintain an increased cardiovascular risk even after cure of the disease. However, the impact of Cushing's disease on renal function remains to be quantified. OBJECTIVES: To evaluate glomerular filtration rate (GFR) and to identify predictors of GFR in patients with Cushing's disease. DESIGN AND METHODS: We conducted a matched case-control study: 18 patients with active or cured Cushing's disease were compared with healthy population controls matched for age and sex. The main outcome measures were GFR and micro-albuminuria. RESULTS: Patients with Cushing's disease had a lower GFR, as measured by 24-h creatinine clearance (79 versus 95 ml/min per 1.73 m2, P = 0.005) and estimated by the MDRD2 formula (75 versus 88 ml/min per 1.73 m2, P = 0.008). Multiple regression analyses indicated that disease duration was the strongest predictor for a worse GFR. The prevalence of micro-albuminuria was low (5.5% in both groups). CONCLUSIONS: Patients with Cushing's disease have a decreased GFR. Even if they are cured, close follow-up with strict control of cardiovascular risk factors and monitoring of GFR seems mandatory. Furthermore, the dosage of certain drugs should be adapted to the individual GFR.

Discrepancy between prolactin (PRL) messenger ribonucleic acid and PRL content in rat fetal pituitary cells: possible role of dopamine.

Data are controversial concerning the time when PRL-synthesizing cells are detected for the first time in the rat pituitary. Using a very sensitive immunocytochemical technique, we could visualize only a few PRL cells before day 10 after birth. At that time, pituitary PRL was still 200 times less abundant than in the adult (on a tissue weight basis) whereas PRL mRNA per mg total RNA was only 80 times lower than in the adult. However, by in situ hybridization, we could demonstrate the presence of PRL mRNA in cells from fetal day 18 on. We have also followed the expression of GH gene in rat pituitary cells during development. In contrast to results obtained with PRL cells, quantitative analysis of cDNA probe hybridization to GH mRNA correlated well with measurements of immunostained cells. We found that PRL was released in the blood from fetal day 19 onwards. Thus, at that time PRL is synthesized and secreted but not stored. We therefore measured brain dopamine levels, and the data support the idea that the rise in dopamine levels after birth contributes to PRL storage. We confirmed in vitro that newborn pituitary cells can store PRL when cultured in the presence of dopamine.

[Scientific education of the candidate specialist in training]. / De wetenschappelijke vorming van de kandidaat specialist in opleiding.

Scientific education is an essential component of the post-graduate training. Fluency in the language of sciences is necessary to understand scientific progress and to translate new scientific advances at the level of medical practice. To reach this goal, specific research skills and participation in research projects should be introduced in postgraduate training. Lack of dedicated time and interest are major barriers in implementing systematically research in the curricula. Some suggestions are made in order to improve research training in the postgraduate programs.

Prolactin cell subpopulations separated on discontinuous Percoll gradient: an immunocytochemical, biochemical, and physiological characterization.

A single-step procedure was devised to separate PRL cells from the rat anterior pituitary gland. After dissociation, cells were centrifuged on a Percoll gradient. Three layers were recovered. The composition of the different layers was evaluated using immunocytochemistry (with antisera to the six pituitary hormones), and in situ hybridization [with DNA complementary to PRL or to GH messenger RNA (mRNA)]. Both methods yielded identical values. PRL cells were recovered in the lower density layer (layer 1) with a good yield (that is 81% of the total PRL cells of the initial cell suspension) and in addition, markedly enriched (indeed 85% of the cells in layer 1 stained for PRL). A second layer (layer 2: intermediate density) contained most of the remaining PRL cells which were, however, heavily contaminated mainly by GH cells and cells that did not stain for any of the known pituitary hormones. A third layer (layer 3: higher density) was enriched in GH cells to 93% (representing, however, only 10% of the initial pituitary GH cells). In addition, PRL and GH were measured by RIA in culture medium and in cell lysates. Hormone biosynthesis was monitored by polyacrylamide gel electrophoresis and autoradiography after culture in the presence of [35S]methionine. These experiments confirmed that layer 1 was enriched in cells containing, and producing, PRL and depleted from GH cells. Cells in layer 2 contained and produced more GH than PRL. PRL cells from layer 1 responded to dopamine and to vasoactive intestinal polypeptide in the same way as PRL cells in the unseparated pituitary cell population. In contrast PRL cells in layer 2 had a lower basal secretion rate but a higher response to vasoactive intestinal polypeptide. Unless this represents a paracrine effect of non-PRL cells, PRL cells in layer 2 exhibit different properties and may therefore form a distinct subpopulation of PRL cells.

Receptors for pituitary adenylate cyclase activating peptides in human pituitary adenomas.

The presence of pituitary adenylate cyclase activating polypeptide (PACAP) receptors coupled to adenylate cyclase was investigated in four types of human pituitary adenomas: three null adenomas and five gonadotropin-, three ACTH-, four GH-, and four PRL-producing adenomas. In all samples, except in prolactinomas, PACAP(1-27) and PACAP(1-38) stimulated adenylate cyclase activity equally well and potently (K(act) around 3 nmol). Vasoactive intestinal polypeptide (VIP) was systematically 100- to 300-fold less potent than both PACAPs. In prolactinomas, PACAP(1-27), PACAP(1-38), and VIP were inactive despite a response of the enzyme to guanosine 5'-triphosphate, Gpp(NH)p, forskolin, and fluoride. [125I-AcHis1]PACAP(1-27) binding was detected in all samples except in prolactinomas. In addition, a detailed analysis of receptors was feasible in all five gonadotropin- and in two ACTH-producing adenomas, confirming the existence of selective PACAP receptors that recognized PACAP(1-27) and PACAP(1-38) with similar high affinity (IC50 0.8-1.5 nmol) and VIP with a low affinity (IC50 100 nmol/L).

Cabergoline in the treatment of hyperprolactinemia: a study in 455 patients.

Cabergoline is a new long-acting dopamine agonist that is very effective and well tolerated in patients with pathological hyperprolactinemia. The aim of this study was to examine, in a very large number of hyperprolactinemic patients, the ability to normalize PRL levels with cabergoline, to determine the effective dose and tolerance, and to assess the effect on clinical symptoms, tumor shrinkage, and visual field abnormalities. We also evaluated the effects of cabergoline in a large subgroup of patients with bromocriptine intolerance or -resistance. We retrospectively reviewed the files of 455 patients (102 males and 353 females) with pathological hyperprolactinemia treated with cabergoline in 9 Belgian centers. Among these patients, 41% had a microadenoma; 42%, a macroadenoma; 16%, idiopathic hyperprolactinemia; and 1%, an empty sella. The median pretreatment serum PRL level was 124 microg/L (range, 16-26,250 microg/L). A subgroup of 292 patients had previously been treated with bromocriptine, of which 140 showed bromocriptine intolerance and 58 showed bromocriptine resistance. Treatment with cabergoline normalized serum PRL levels in 86% of all patients: in 92% of 244 patients with idiopathic hyperprolactinemia or a microprolactinoma and in 77% of 181 macroadenomas. Pretreatment visual field abnormalities normalized in 70% of patients, and tumor shrinkage was seen in 67% of cases. Side effects were noted in 13% of patients, but only 3.9% discontinued therapy because of side effects. The median dose of cabergoline at the start of therapy was 1.0 mg/week but could be reduced to 0.5 mg/week once control was achieved. Patients with a macroprolactinoma needed a higher median cabergoline dose, compared with those with idiopathic hyperprolactinemia or a microprolactinoma: 1.0 mg/week vs. 0.5 mg/week, although a large overlap existed between these groups. Twenty-seven women treated with cabergoline became pregnant, and 25 delivered a healthy child. One patient had an intended abortion and another a miscarriage. In the patients with bromocriptine intolerance, normalization of PRL was reached in 84% of cases, whereas in the bromocriptine-resistant patients, PRL could be normalized in 70%. We confirmed, in a large-scale retrospective study, the high efficacy and tolerability of cabergoline in the treatment of pathological hyperprolactinemia, leaving few patients with unacceptable side effects or inadequate clinical response. Patients with idiopathic hyperprolactinemia or a microprolactinoma, on average, needed only half the dose of cabergoline as those with macroprolactinomas and have a higher chance of obtaining PRL normalization. Cabergoline also normalized PRL in the majority of patients with known bromocriptine intolerance or -resistance. Once PRL secretion was adequately controlled, the dose of cabergoline could often be significantly decreased, which further reduced costs of therapy.

Pit-1/GHF-1 expression in pituitary adenomas: further analogy between human adenomas and rat SMtTW tumours.

Adenomas can develop from each cell type of the anterior pituitary. In the normal pituitary, three of these cells types, the GH-, prolactin- and TSH-secreting cells, express the transcription factor Pit-1/GHF-1 which is responsible for prolactin and GH (and probably TSH) cell commitment, differentiation, probably proliferation and gene expression. We have analysed the expression of Pit-1/GHF-1 in a panel of human pituitary adenomas. All GH-, prolactin- and TSH-expressing adenomas studied expressed the Pit-1/GHF-1 factor, as demonstrated by in-situ hybridization and immunocytochemistry. The expression was higher in adenomas than in normal human pituitary. In contrast, ACTH- and LH-FSH-secreting and non-secreting adenomas were negative. Seven transplants of the spontaneous rat prolactinoma SMtTW were also investigated and all were found to be positive. This further stresses the analogy between these tumours and human prolactinomas. Taken together, the data confirm that Pit-1/GHF-1 expression is restricted to GH-, prolactin- and TSH-expressing cells, and the increased expression in adenomas is compatible with a role of Pit-1/GHF-1 in cell proliferation.

Prolactin and growth hormone mRNA and protein characterization in SMtTW rat pituitary tumours.

We have combined different techniques to analyse passages of five different rat spontaneous pituitary tumours (SMtTW) that were transplanted under the kidney capsule. These tumours were secreting prolactin (PRL), GH or both hormones. RIA, immunocytochemistry (ICC) and Western blot analysis were applied to characterize the hormone(s) stored (ICC and Western blot) and secreted (RIA). mRNA content was analysed by PCR, Northern blot analysis and in situ hybridization. The data point not only to the reliability of the techniques used at both protein and RNA levels for each tumour studied but also to the complementarity of some techniques. For example, whereas Northern blot analysis demonstrates the presence and size of hormone mRNA, in situ hybridization indicates the percentage of cells expressing a given hormone mRNA and allows the presence of one population (or more) of cells in a given tumour to be identified. Moreover, the tumours were compared with normal rat pituitary. Although the PRL and GH mRNAs were identical in size, the amount of mRNA was lower in the tumours. At the protein level, the PRL and GH variants exhibited a different pattern of expression in tumours compared with the normal rat pituitary. The biological significance of these differences is discussed.

Expression of SOCS genes in normal and leukemic human leukocytes stimulated by prolactin, growth hormone and cytokines.

To evaluate the possible role of the recently described family of suppressors of cytokine signaling (SOCS) factors in the human lympho-hemopoietic system, we have monitored SOCS factor expression, both constitutive and induced by either cytokines, prolactin (PRL) or growth hormone (GH), using polymerase chain reaction in normal and leukemic cells. CIS (cytokine-inducible SH2-containing protein), SOCS-2 and SOCS-3 were constitutively expressed in peripheral blood mononuclear leukocytes. SOCS-3 expression was enhanced by PRL or by IFN-gamma. In bone marrow cells and granulocytes, CIS expression was induced and SOCS-2 enhanced by IFN-gamma and by PRL. In tonsillar cells, CIS expression was increased and SOCS-2 was induced by IL-1beta, IL-6, PRL and GH. SOCS-3 expression was enhanced by IL-1beta. The expression of SOCS-7 was increased by IL-6, PRL and GH. In Raji B-lymphoma cells, the expression of SOCS-2 and SOCS-7 was enhanced by IL-1beta. In THP-1 myeloid leukemia cells pretreated with TPA (to induce receptors for IFN-gamma), IFN-gamma induced SOCS-2. Jurkat cells expressed more SOCS-2 when exposed to PRL. Original observations in this work include the first report on SOCS-7 induction by cytokines. Also our data shed new light on the possible involvement of PRL and GH in the cytokine network. These hormones could modulate the transduction of signals originating from receptors for various cytokines.

Postnatal development of growth hormone and prolactin cells in male and female rat pituitary. An immunocytochemical light and electron microscopic study.

Localization and ultrastructural maturation of prolactin (PRL) and growth hormone (GH) cells were studied in pituitaries from neonatal, immature (4-6 weeks old), and adult rats (2-3 months old) by light and electron microscopic immunocytochemistry. The distribution pattern of these cells did not change with age. Both cell types were concentrated laterodorsally, with PRL cells adjacent to the intermediate lobe and GH cells nearer the center of the pars distalis. Labeling density of the immunogold reaction was highest for both hormones in immature rats. In neonatal and immature rats, one PRL cell type with granules 200 nm in diameter was present. In adult rats, two types of PRL cells were present: one containing polymorphous granules measuring about 500 nm (prevalent in female rats), the other with spherical granules about 200 nm (prevalent in male rats). No changes were detected in GH cells during maturation.