Mouse strain (STS/A) resistant to mammary tumor induction by hypophysial isografts.

Implantation of hypophysial isografts does not lead to induction of mammary tumors in all strains of mice lacking the exogenous murine mammary tumor virus. While O20, C3Hf, and BALB/c females are highly susceptible and C57BL and TSI females are of intermediate susceptibility, the STS females appear to be nearly totally resistant. The resistance of the STS strain is not due to failure of prolactin production by the hypophysial isografts and may therefore be due to a genetically controlled mechanism at target cell level. Neither resistance, i.e., low incidence of mammary tumors (2% in STS), nor susceptibility, i.e., high incidence at low age (93% at 349 days in C3Hf; 83% at 360 days in BALB/c), is dominant. F1 hybrids of strain STS and the two strains C3Hf and BALB/c show high incidences (STS X C3Hf F1, 90%; STS X BALB/c F1, 60%), but the age at which tumors appear (476 and 604 days, respectively) is much higher, suggesting that more than one gene is involved in this type of hormonal carcinogenesis of the mammary gland in mice.

Studies on the irreversible nature of prolactin binding to receptors.

Studies on hormone-receptor interactions generally assume that the formation of a hormone-receptor complex is a reversible process. This assumption has been examined directly in three experiments using liver membrane receptor preparations from pregnant rats and ovine PRL (oPRL). In Exp 1, Receptors were preincubated with a range of concentrations of oPRL at 23 C for periods up to 60 min, washed thereafter to remove free oPRL, and subsequently incubated with [125I]iodo-oPRL (23 C) to determine specific binding. Preincubation of receptors (0.25 mg membrane protein) with oPRL (5 ng) for periods as brief as 10 min reduced subsequent binding of [125I]iodo-oPRL to receptor, suggesting incomplete dissociation of oPRL even after 30 h. In Exp 2 after preincubation for 30 min with oPRL and subsequent incubation with [125I]iodo-oPRL for 19 h, membranes were washed, and the dissociation (23 or 37 C) of [125I]iodo-oPRL from the hormone-receptor complex in the presence or absence of 1000 ng oPRL was studied. After 48 h, only 35-50% of the [125I]iodo-oPRL dissociated from the hormone-receptor complex even in the presence or excess oPRL, indicating a heterogeneity of binding sites (i.e. 50-65% irreversible; 35-50% reversible). When pregnant rat serum was used in place of oPRL or when rabbit mammary glands were used instead of rat livers to prepare receptor preparations, results were similar to those described above, except for the nearly complete dissociation (90%) obtained at 37 C using rabbit mammary gland receptors. In Exp 3 after incubation (10 min, 2 h, or 15 h) of rat liver receptors with [125I]iodo-oPRL plus various amounts of oPRL, the hormone-receptor complex could be completely dissociated with 5 M MgCl2, restoring binding affinity and capacity of receptor to their original values. Labeled oPRL dissociated by MgCl2 treatment from such a complex is capable of binding to fresh receptor. These data strongly suggest that the PRL-receptor interaction, particularly the rat liver receptor interaction with PRL under usual in vitro conditions, is not reversible to a significant degree. This is not due to hormone or receptor damage but to a significant number of binding sites (50-65%) in the receptor preparation which are not reversible except under extreme conditions.

Prolactin inhibition test with L-dopa: decrease and restoration of plasma prolactin levels in the rat by a peripheral process.

L-DOPA, within 30 min after administration, induced a highly significant decrease of plasma prolactin levels (phase 1) in a number of groups of rats, differing in age and/or endocrine status, apparently by direct inhibition of prolactin release from the pituitary. Three hours after administration of L-DOPA these low plasma prolactin concentrations in treated animals had increased (phase 2) and did not differ significantly from levels in control animals, indicating that the effect of L-DOPA on plasma prolactin levels is only of short duration. During this process some interesting phenomena were observed, especially in the animals treated with oestrone. The elimination rate of prolactin from plasma was very high (t 1/2 = 2.8 min), as indicated by decreasing concentrations of the hormone during phase 1. Pituitary prolactin content did not change during phase 1, suggesting that prolactin synthesis was also stopped. Notwithstanding the high elimination rate, plasma prolactin regained initial concentrations in phase 2, suggesting release of a substantial part of the pituitary prolactin content. The latter,however, remained constant during the whole experiment (i.e. before L-DOPA administration and during phase 1 as well as phase 2). The results suggested another working mechanism of L-DOPA in decreasing plasma prolactin levels, namely by stimulating the uptake of this hormone in the periphery. After the effect of L-DOPA had ceased, most of the prolactin from the periphery returned into the bloodstream, causing a rapid restoration of plasma prolactin levels without substantial release from the pituitary. The nature of the processes responsible for the peripheral uptake of prolactin is discussed.

Prolactin stimulation test with perphenazine: an evaluation of plasma prolactin levels and pituitary secretory activity in the rat.

Many investigations of the regulation of prolactin synthesis and release are based on single plasma prolactin determinations. The purpose of the present experiment was to ascertain whether groups of rats (i.e. young or adult, male or female animals, being either intact, gonadectomized or gonadectomized and treated with oestrone), differing in age and/or endocrine status, will react to a single dose of perphenazine by an acute release of pituitary prolactin in proportion to their initial plasma prolactin levels. No consistent relation existed between the classification of the twelve groups of rats into three categories of basal plasma prolactin levels (i.e. less than 20, 25-50, greater than 125 ng/ml) and their response to perphenazine. Even though all groups showed a highly significant increase of plasma prolactin levels the magnitude of the maximum prolactin response at 30 min varied greatly within the groups of one category and thus was not related to the initial prolactin levels. The effect of 14 days of oestrone treatment in increasing plasma prolactin levels in gonadectomized animals was greatest in young and adult male rats, less in young females and not significant in adult females. The results obtained after perphenazine treatment in the latter group made it clear that the effect of oestrogen treatment on prolactin release can be completely blocked by increasing synthesis and/or release of the prolactin-release inhibiting factor (PIF). Since perphenazine induces decrease of pituitary prolactin and a concomitant increase of plasma prolactin levels through lowered PIF-action, the positive effect of oestrogens on prolactin release (as observed in gonadectomized male and young female rats) apparently is caused by a different mode of action. The implications of these findings for the regulation of prolactin release, as affected by the endocrine status of the rat, is discussed. Moreover, comparison of prolactin lost from the pituitary and gained in the circulation of the experimental animals, with amounts of prolactin that were observed to disappear from plasma during the experiment, provided suggestive evidence that the capacity to synthesize and/or eliminate prolactin, after a sudden provoked release of the hormone, differed among the groups. The rates of synthesis by the pituitary, of release from the pituitary into the circulation as well as of elimination of the hormone from the circulation (equally involved in determing actual plasma levels) are thought, therefore, to be far more important for the elucidation of prolactin regulation than single plasma prolactin determinations.

Prolactin binding in benign and malignant mammary tissue of female dogs.

Prolactin receptor (PRL-R) concentrations were determined in membrane preparations of canine mammary tumours and of non-affected mammary tissues by a radioreceptor-assay using ovine prolactin (oPRL) both for 125I-labelling and for displacement. Receptor levels greater than or equal to 3 fmol/mg membrane protein were considered positive. Histologically non-affected samples of mammary tissue from 6 dogs were PRL-R positive (12-195 fmol/mg protein). These levels were positively correlated with epithelium content (based on surface area in microscopic sections; r = 0.943, P less than 0.02). In tumour samples where pre-existing mammary epithelium (PME) was present (3 non-malignant and 6 malignant tumour samples; PME content 5-10%), the cut-off limit for PRL-R positivity was increased to 50 fmol/mg protein to forestall false positives due to non-affected tissue. If no PME was present the general limit of 3 fmol/mg protein was maintained. All 18 non-malignant tumours showed PRL-R (18-162 fmol/mg protein). The PRL-R levels were positively correlated with levels of oestrogen-(ER; r = 0.735, P less than 0.002) and progesterone receptors (PgR; r = 0.556, P less than 0.02) as measured by a multi-concentration dextran-coated charcoal method. ER and PgR levels were also proportional (r = 0.660, P less than 0.01). In 6 dogs bearing primary cancers with 5-10% PME, 1 out of a total of 6 tumours was PRL-R positive. In 9 dogs bearing primary or locally recurrent cancers without PME, significant PRL-R levels were measured in 2 out of a total of 10 tumours. Three metastatic sites in 2 other dogs were PRL-R positive. In 2 dogs (1 with a PRL-R negative local recurrence) the metastatic lesions were PRL-R negative. Thus 5 dogs of a total of 18, had PRL-R positive mammary cancers (3-377 fmol/mg protein). Unlike in non-malignant lesions the ER, PgR, and PRL-R levels were not related. In mammary cancer the presence of PRL-R was less common (P less than 0.001), and the ultimate levels less high (P less than 0.001) than in non-malignant tumours. In comparative studies using pooled membrane preparations from benign mammary tissues, oPRL was far more effective than canine prolactin (cPRL) in displacing 125I-oPRL; canine growth hormone (cGH) in this respect was ineffective. It is concluded that non-malignant mammary tissue in the dog generally is PRL-R positive; only some mammary cancers retain the PRL receptors.

Internal regulation of a modular system: the different faces of internal control.

The living cell houses a multitude of molecular processes that operate simultaneously in a mutually consistent fashion. A certain degree of organization stands out, e.g. in terms of the various metabolic pathways, transcription versus translation, signal transduction versus metabolism. This paper shows that by taking one of the aforementioned organizational principles into account, the complexity of understanding cell function quantitatively may be reduced significantly. To this aim the definition of the corresponding type of organization is refined and the conceptual tools used in the analysis of the control of cell function are adjusted. The approach is elaborated for a theoretical model of cell function, in which the latter depends on a constellation of interdependent but unconnected modules. The organization of a system is reduced to global control within a limited set of partaking modules and the links between them. Information about the systems total internal control and regulability is then drastically reduced to the information specifying global control and the regulability of the pathways that constitute the system. It is shown quantitatively how control at a lower level of organization bears on the control of the cell as a whole. The approach centers on writing the product of control (matrix) and elasticity (matrix) at a number of different levels of aggregation; these products equalling the identity (matrix) under different conditions. We demonstrate that there are at least three ways in which control and regulability of a system can be matched. In one, the true control within and between the modules of the systems is the inverse of the primary regulability (i.e. elasticity plus stoichiometry). In a second, the control internal to a module (but partly determined through the other modules) is matched by the inverse of newly defined 'global' regulabilities for each module separately, which comprise the regulatory impact of the remainder of the system. In the third, the regulabilities are the ones intrinsic to the module and the control is taken equal to the control that would reign in the absence of the regulatory interactions between the units. In making these distinctions, it becomes transparent how much control stems from control within the organizational modules, and how much derives from the regulatory interactions between them. Control through other modules turns out to be equivalent, at steady state, to control within a module. The implications of this type of cellular organization for the location of the steady-state operating point is discussed.

Progesterone and the control of functional luteolysis, of secretion of prolactin and of pituitary LHRH responsiveness. A study with pseudopregnant rats kept in alternating and constant lighting conditions.

The effect of exogenous progesterone (P) on the corpus luteum function (in terms of the secretion of P and 20-alpha-dihydroprogesterone (DHP), on the secretion of prolactin (Prl) and on the pituitary responsiveness to LHRH was studied in pseudopregnant (PSP) rats kept in alternating and constant lighting conditions (LD-PSP and LL-PSP rats, respectively). Rats were rendered pseudopregnant by appropriately timed stimulation of the cervix uteri (LL rats first received an ovulatory dose of hCG). LH responses were induced by constant rate infusion of LHRH (104 ng/h for 21 h). P was delivered by subcutaneously inserted Silastic implants; control rats received sham implants. In both LD-and LL-PSP rats the plasma P and DHP levels were high on day 8 of PSP. On day 12, however, the plasma P levels had fallen but the DHP levels had risen, demonstrating that between days 8 and 12 functional luteolysis had occurred and that neither the production of P and DHP, nor the timing of luteolysis are under the control of the lighting conditions. On day 12 of PSP the pituitary responsiveness to LHRH was much higher than on day 8. Moreover, on days 8/9 of PSP peaks of Prl were seen in all rats, but on days 11/12 such peaks were largely absent. In LD-PSP rats 'nocturnal' Prl peaks were seen on days 8/9 in all 9 experimental animals, but 'diurnal' peaks were seen in only 4 of these animals. Also, the diurnal peaks were on average much lower than the nocturnal peaks.(ABSTRACT TRUNCATED AT 250 WORDS)

Monoclonal antibody 123C3, identifying small cell carcinoma phenotype in lung tumours, recognizes mainly, but not exclusively, endocrine and neuron-supporting normal tissues.

Monoclonal antibody (MAb) 123C3 was raised against a membrane preparation of a small cell lung carcinoma (SCLC) specimen and its reactivity on normal tissues was tested. For the endocrine system, positive tissues included: pituitary and adrenal glands, thyrocytes and C-cells of the thyroid, the parathyroids, testis Leydig cells and pancreatic islets. In bronchioles and intestinal epithelium occasional cells, resembling Kultchitsky and enterochromaffin cells, were also positive. Epithelia like rete testis, mammary epithelium and gastric mucosa were positive in all or a significant proportion of cells. The positive cells in mammary epithelium and gastric mucosa were too numerous to represent the endocrine cells only. Neurons were usually negative or weakly positive. Their supportive cells such as glial, Schwann and ganglionic satellite cells were positive. Mesenchymal cell types, such as smooth muscle cells in most organs, cardiac muscle cells, the pia-arachnoid and ovarian stroma cells were positive, indicating that 123C3 reactivity is not confined to epithelial and neuron-supporting tissues. In Western blots of tumour specimens 123C3 recognized a 29 kDa band in reducing conditions, shifting to approximately 150 kDa in non-reducing conditions. Immunofluorescence on live tissue culture cells demonstrated presence of the antigen on the cell surface.

Presence of immunoreactive growth hormone and prolactin in the ovine pineal gland.

The use of antisera raised against bovine growth hormone (GH) and ovine prolactin (PRL) enabled the detection of related immunoreactive (ir) sequences of proteins in ovine pineal tissue. The isolation of PRL-like ir-material was accomplished using a 0.25 M ammonium sulphate (pH 5.5) extraction followed by ethanol precipitation, whereas the resulting 2.0 M ammonium sulphate (pH 7.0) precipitate contained a GH-like immunoreactivity. Gel chromatography of the GH-like immunoreactivity (Sephadex G-100) indicated the presence of several GH-like fragments ranging in the M(r) range of 7,000 to 55,000. Analyses of the PRL-like ir-material found in pineal tissue on HPLC using a TSK 545-DEAE column led to the resolution into a single peak of immunoreactivity. A single peak of activity was also observed following chromatofocusing and hydrophobic interaction chromatography of the ir-peak from the TSK 545-DEAE column. The PRL-like ir-material inhibited the binding of [125I]ovine PRL-S14 to anti-ovine PRL antibodies without showing an affinity for binding to anti-rat PRL or anti-bovine GH antibodies. Scatchard analysis of the binding of pineal PRL-like ir-material and pituitary ovine PRL-S14 to liver membranes from day-20 pregnant rats revealed similar affinity constants (Ka of 4.7 +/- 0.2 x 10(9) M-1). In addition, the replication of Nb 2 Node rat lymphoma cells was stimulated by pineal PRL-like ir-material, an effect known to be specific for lactogenic hormones. The pineal PRL-like immunoreactivity appeared on sodium dodecyl sulfate polyacrylamide gels as a single major band of M(r) 24,000. The functional status of PRL- and GH-like ir-material in the ovine pineal remains to be determined, but evidence is presented that the overall protein synthesis rate of the rat pineal responded to circulating concentrations of PRL.

Abnormalities in evening plasma prolactin levels in nulliparous women with benign or malignant breast disease.

In the present study the assay results of prolactin concentrations in serial samples of blood obtained from premenopausal women with benign or malignant disease of the breast are compared with--and discussed in relation to--findings reported in earlier studies based on single samples of blood taken at various times from a large and ostensibly normal population of women. The finding of an abnormality in nycthemeral prolactin levels in the established disease is considered to strengthen the concept that the same abnormality found in high-risk groups is of aetiological importance.