Receptor Density Determines Secretory Response Patterns Mediate by Inositol Lipid-Derived Second Messengers

Relationship between cytokeratin staining patterns and clinico-pathological features in somatotropinomae

OBJECTIVE

Somatotropinomae are classified as densely and sparsely granulated adenomae, which typically exhibit a perinuclear pattern (PP) and a dot pattern (DP) in cytokeratin (CK) immunostaining respectively. Some exhibit a mixed pattern (MP). We studied the relationship between these somatotropinoma subtypes and their clinico-pathological features.

METHODS

The study population consisted of 141 Japanese acromegalic patients. We evaluated their clinical presentation and their response to provocation tests with TRH and LHRH and to suppression (octreotide) test. Tumour tissues were subjected to immunostaining for CAM-5.2, MIB-1, CD34, E-cadherin (CDH1) and p53 (TP53). In 43 cases (30 non-DP and 13 DP), we analysed gsp mutations (constitutively activating mutations of the G(s)α protein that is encoded by GNAS gene).

RESULTS

The 141 adenomae were categorised into three subtypes based on their CK staining patterns; 30 (21.3%) exhibited DP, 83 (58.9%) exhibited PP, and 28 (19.9%) exhibited MP. Compared with the other subtypes, DP adenomae were significantly larger, and their E-cadherin expression and response to TRH, LHRH and octreotide challenge were lower. The postoperative cure rate tended to be lower in DP adenomae. gsp mutations were detected in 25 of 43 cases examined (58.1%); 20 of the 30 non-DP (66.7%) and 5 of the 13 DP tumours (38.5%) were affected by the mutation.

CONCLUSION

DP somatotropinomae exhibit characteristic features. Compared with the non-DP subtypes, DP adenomae manifested a larger tumour size, a lower incidence of abnormal responses to TRH and LHRH challenge, a poor response to octreotide test and a lower expression of E-cadherin. gsp mutation was not exclusive for non-DP somatotropinomae.

Organization of the receptor-mediated phosphoinositide cycle: relationship between receptor occupancy and accession of phosphatidylinositol

We have previously reported the existence of separate hormone-responsive and -unresponsive pools of inositol phospholipids in WRK-1 cells. In order to further explore this concept, we have performed experiments to examine the relationship between the plasma membrane receptor and the pool of phosphatidylinositol (Ptdlns) that is metabolized in response to hormonal stimulation. The results support the following conclusions. 1) The amount of Ptdlns metabolized in WRK-1 cells in response to vasopressin is proportional to the number of receptors occupied; neither prolonged activation with nor readdition of submaximal concentration of vasopressin induced the same degree of Ptdlns metabolism as maximal concentration of vasopressin. 2) Dissociation of cytoskeletal structures by incubation with cytochalasin D did not alter the amount of Ptdlns accessed during hormonal stimulation. 3) Accession of Ptdlns from internal membranes does not depend on internalization and recycling of the receptor; cells incubated in potassium-free medium failed to internalize receptor-ligand complexes, yet they accessed the same amount of Ptdlns in response to vasopressin as did control cells. 4) Golgi-mediated phosphatidylinositol transport is not involved in hormone-stimulated phosphoinositide turnover, since brefeldin A, which interferes with Golgi-mediated transport processes, had no effect on the amount of Ptdlns accessed during vasopressin stimulation. 5) Phosphoinositide breakdown and compensatory resynthesis is not a closed process; newly synthesized Ptdlns is not preferentially localized to a hormone-responsive pool but is generally redistributed between responsive and unresponsive pools.

Response of rat salivary glands to mastication of pelleted vitamin A-deficient diet

Interpretation of previous studies of the effects of hypovitaminosis. A on salivary glands is confounded by the atrophic effects of liquid or powdered diets. The purpose of this study was to reevaluate the effects of vitamin. A deficiency on the morphology and function of rat salivary glands using a pelleted diet that promotes physiological levels of masticatory stimulation. Profound vitamin A deficiency resulted in a marked decrease in stimulated parotid secretion. Histological evaluation demonstrated the development of squamous metaplasia in the ducts of parotid, submandibular and sublingual salivary glands; however, atrophy was observed only in serious salivary glands. In the parotid gland the degree of atrophy corresponded to the decrease in stimulated secretion. Mild hypovitaminosis A (before the development of squamous metaplasia in ducts) was associated with distinctly different effects. The parotid gland was moderately enlarged. There was also a significant increase in stimulated secretion, which was not explained by changes in gland size, muscarinic receptor number or affinity, or receptor-mediated calcium signalling.

Angiotensin II and bradykinin stimulate phosphoinositide breakdown in intact rat kidney glomeruli but not in proximal tubules: glomerular response modulated by phorbol ester

We have investigated the effect of angiotensin II, bradykinin, insulin and insulin-like growth factor I on phosphoinositide turnover in intact rat glomeruli and tubules. Angiotensin II produced a dose-dependent increase in inositol monophosphate formation with an IC50 of 10(-7)M, when added to isolated rat glomeruli. Angiotensin II-stimulated inositol phosphates formation was inhibited by the angiotensin receptor antagonist [Sar-Leu8]angiotensin II, indicating that the above response was mediated through activation of an angiotensin receptor in intact glomeruli. Besides angiotensin, in intact glomeruli, only bradykinin stimulated a phosphoinositide response, while in intact proximal tubules, none of the agonists tested produced an activation of the inositol phosphate formation. Angiotensin II- and bradykinin-stimulated inositol phosphate accumulation in intact glomeruli was inhibited by phorbol myristate acetate, an activator of protein kinase C.