Absence of 5 alpha-reductase activity in the gubernaculum during descent of the fetal pig testis.

To evaluate the hypothesis that testicular descent is mediated by the action of high local concentrations of dihydrotestosterone in the gubernaculum, testis, or epididymis, we obtained tissues from 30 male pig fetuses between 63 and 101 days of gestation. We assayed the 5 alpha-reductase activity in homogenates of pooled tissue by following the conversion of (3H)testosterone to (3H)dihydrotestosterone. The 5 alpha-reductase activity in the urethra and prostate increased prior to and during, but decreased after, the period of testicular descent. The 5 alpha-reductase activity in the gubernaculum remained constant throughout gestation and was not significantly higher than the background activity found in umbilical cord, testis plus epididymis, striated thigh muscle and heat inactivated samples of prostate and urethra. Prior to testicular descent, the 5 alpha-reductase activity was approximately 60 to 300 times higher in the urethra than in the gubernaculum, and approximately 20 to 55 times higher in the prostate than in the gubernaculum. These findings indicate that local conversion of testosterone to dihydrotestosterone in the gubernaculum or epididymis does not play a role in the mediation of testicular descent in the pig fetus.

Partial purification of human prostatic 5 alpha-reductase (3-oxo-5 alpha-steroid:NADP+ 4-ene-oxido-reductase; EC 1.3.1.22) in a stable and active form.

Human hyperplastic prostate tissue was homogenised in high ionic strength buffer and the post nuclear homogenate was incubated with 0.8% octyl glucoside and bovine brain lipids. Dialysis of the resulting liposome suspension yielded a preparation in which 5 alpha-reductase was active and stable for at least three weeks and showed an increase in specific activity (Vmax +/- SD = 48.9 +/- 7.4 pmol DHT/mg protein/ml) over that of the starting homogenate (Vmax +/- SD = 5.6 +/- 1.5 pmol DHT/mg protein/min) of 8.7 times.

Growth regulation of cancer metastases by their host organ.

We analyzed mechanisms responsible for organ-specific metastasis by using two melanoma sublines derived from the same mouse tumor, of which one colonizes the lungs (F10) and the other colonizes the liver (L8) after intravenous injection. Both lines were obtained by selective growth in lung or liver after injection of tumor cells into a tail vein or portal vein. Contrary to common concepts, the cells of the liver-colonizing melanoma line do not accumulate preferentially in the liver after intravenous administration in vivo. However, the selective survival and proliferation of these melanoma cells in the target organ (liver) may be explained by the unexpected observation that they can be specifically stimulated to proliferate in the presence of hepatocytes, whereas the cells of the lung-colonizing line cannot. Growth promotion under coculture conditions in vitro was monitored both by thymidine incorporation into DNA and by increase in cell numbers. The proliferative stimulus is not mediated by an easily diffusible factor but rather depends upon direct contact between liver cells and those tumor cells that metastasize to that particular organ.

Effects of altering surface glycoprotein composition on metastatic colonisation potential of murine mammary tumour cells.

This study has examined cells from naturally-occurring murine mammary tumours to ascertain whether cell surface glycoproteins play a significant role in colonisation of the lungs after intravenous inoculation. It was found that gel electrophoretic analysis of membrane extracts and lectin adsorption studies did not reveal any consistent differences in glycoprotein composition of cells from tumours which can heavily colonise the lungs relative to ones from tumours which cannot do so or to cells from pulmonary metastases. Also, alteration of structural and functional properties of surface glycoproteins by treatment with succinylated lectins or with drugs such as tunicamycin and swainsonine, which inhibit glycosylation of membrane proteins, had no specific effects on metastatic colonisation of the lungs. Tunicamycin apparently decreased capability to form experimental metastases but also diminished tumourigenicity on subcutaneous inoculation, although it did not affect tumour cell viability in vitro. This information supports earlier studies from this laboratory involving enzymic digestion of the surface of living tumour cells before inoculation and demonstrates that the pulmonary colonisation capability of these mammary tumour cells can withstand global disorganisation of membrane glycoprotein structure and composition. This implies that either the surface glycoproteins are not important in the colonisation process, or that these tumour cells have great capability for rapid repair of their surfaces. It is concluded that a clear answer to whether surface glycoprotein composition has a decisive role in pulmonary colonisation by these mammary tumour cells requires introduction of stable heritable traits into tumour cell populations by genetic manipulation.

Effect of enzymic removal of cell surface constituents on metastatic colonisation potential of mouse mammary tumour cells.

Trypsin treatment of viable cells from 24 spontaneous murine mammary carcinomas resulted in a mild but reproducible diminution in their capability to colonise the lung after i.v. reinoculation but did not alter the distribution of deposits formed. The effects were similar on tumours of high and of low colonisation potentials. Neuraminidase and hyaluronidase did not exert any effect on metastatic colonisation potential, although all 3 enzymes were shown to be active and specific in cleaving their purified substrates, under the conditions in which they were used on the cells. Trypsin and neuraminidase were also shown to release characteristic components from the surfaces of living tumour cells, although hyaluronidase did not release detectable quantities of N-acetyl glucosamine indicating that there is little hyaluronic acid-related mucopolysaccharide on the surface of these mammary tumour cells. The results provide direct evidence suggesting that surface protein composition exerts an effect on the metastatic colonisation capability of mammary tumour cells.

Binding of 125I-labelled concanavalin A by cells from spontaneously arising murine mammary carcinomas and experimentally induced metastases.

Measurement of the quantity of 125I-labelled Concanavalin A bound by disaggregated cells from a series of 20 primary murine mammary carcinomas has shown that there is no relationship between the binding of this lectin and capability of the cells to colonise the lungs after intravenous injection. However, cells taken from pulmonary deposits formed by those tumors able to colonise the lungs consistently bound greater amounts of the radio-labelled lectin than cells from the corresponding primary tumour (paired t-test, p less than 0.05). Also cells obtained from tumours formed by transplantation of pulmonary deposits into the mammary fat pad bound still more of this lectin than cells from either corresponding pulmonary deposits or primary tumours. The findings indicate that the higher lectin binding characterising cells from metastatic deposits is not site-induced and may reflect either a selective advantage of cells with these properties for metastasis formation or phenotypic changes in the cells during the metastatic process.

The relationship between chemical structure and the in vivo metabolism of an homologous series of n-alkyl carbamates.

The metabolism and pharmacokinetics of carbonyl [14C] labelled ethyl, n-butyl, n-hexyl and n-octyl carbamates has been examined in rats after oral and intravenous administration. Hydrolysis of the carbamate group was a major metabolic fate, particularly of the more water soluble carbamates. Conversely, with increasing lipophilicity increasing amounts of omega-1 oxidation products were found both in plasma and urine. The plasma pharmacokinetic data could not be explained by a simple bi-exponential model, ethyl carbamate in particular showing unexpectedly persistent blood levels. A model has been proposed to explain the pharmacokinetic data for ethyl, n-butyl, n-hexyl and n-octyl carbamates. The essential features of this model are that carbamate is thought not to be in equilibrium between the peripheral and central compartment and that hydrolytic metabolism takes place in the peripheral compartment while oxidative metabolism to urinary metabolites occurs in the central compartment.

Rapid absorption from the urinary bladder of a series of n-alkyl carbamates: a route for the recirculation of drugs.

1 The rate of loss of a series of n-alkyl carbamates from the lumen of the urinary bladders of female rats has been studied. 2 The rate of loss obeys first order kinetics and was not affected by water flux across the bladder wall nor by binding of the carbamates to it. 3 The rate of loss of octyl carbamate was reduced by about 76% by the presence of 5% Tween 80. Histological evidence indicates that this may be due to the formation of a thin luminal lining which may be adsorbed Tween 80 or mucopolysaccharide material. 4 The absorption rate of the carbamates was limited by their hydrophilicity but reached a plateau for the more lipophilic homologues with a half life for loss of approximately 10 min. 5 The implications of these results with regard to the recirculation of unmetabolized drugs and hydrolysed conjugates of drugs, the systemic absorption of intravesically applied cancer chemotherapeutic agents and bladder wall permeability to carcinogens are discussed.