Suppression of rat mammary cancer development by N-(4-hydroxyphenyl)retinamide (4-HPR) following surgical removal of first palpable tumor.

A study was conducted to determine whether N-(4-hydroxyphenyl)retinamide (4-HPR) affects the development of new mammary tumors subsequent to the surgical removal of the first palpable tumor. Sprague-Dawley female rats were injected i.v. with 35 mg N-methyl-N-nitrosourea (MNU) per killogram body weight at 50 days of age. The first palpable tumor was removed when 0.3-0.5 cm in diameter, and the animals placed on diets containing either 1, 2 or 3 mmol 4-HPR/kg diet. Placebo diet without 4-HPR served as control. Some animals were killed at the time of surgical removal of the first tumor and whole mounts of the mammary glands were prepared. Moreover, five animals per group were bled at 1, 3 and 6 months after commencing the 4-HPR diet and the levels of 4-HPR and N-(4-methoxyphenyl)retinamide (4-MPR) were determined. 4-HPR decreased tumor multiplicity in a dose-related manner, but cancer formation was only inhibited at the 2 and 3 mmol levels of 4-HPR. Whole mounts of mammary glands of rats treated with MNU demonstrated the presence of nonpalpable microscopic tumors in addition to the palpable tumor which was excised. Plasma levels of 4-HPR and 4-MPR increased with increasing dietary dose levels, but a linear relationship was not evident. However, the increase in plasma 4-HPR was directly correlated with an increased survival of the tumor-bearing animals. The results indicate that 4-HPR effectively inhibits the appearance of subsequent mammary tumors following excision of the first palpable tumor, and thus may be suitable for use as a chemopreventive agent in patients at increased risk for breast disease.

Stability of Aroclor 1254-induced rat liver postmitochondrial supernatant (S-9) following long-term storage (-75 degrees C).

The stability of Aroclor 1254-induced rat liver postmitochondrial supernatant (S-9) over a 5-year period was investigated in a retrospective study. S-9 was uniformly prepared at 6-month intervals, and aliquots were stored at -75 degrees C. The protein and cytochrome P-450 content of these lots of S-9 were very similar, and no differences attributable to duration of storage were observed in the activities of ethoxycoumarin O-deethylase, aniline hydroxylase, cytochrome P-450 reductase or aryl hydrocarbon hydroxylase. There was no decrease following 5 years of storage in the ability of S-9 to activate 2-aminoanthracene, as measured in the Ames test (TA98), but there was a notable reduction following more than 1 year of storage in the ability of the S-9 to generate Ames test activity with benzo(a)pyrene. Based on the results of these studies, S-9 prepared and stored under these conditions appears to be suitable for use in vitro genotoxicity assays for at least 1 year.

The effect of hydralazine on arachidonic acid metabolism in isolated, washed human platelets.

The effects of hydralazine on arachidonic acid metabolism were studied in isolated washed human platelets. The washed platelets (10(9)/ml) were exposed to 14C-arachidonic acid and incubated for 15 minutes in a platelet aggregometer (37 degrees C). The media was then extracted and the reaction products separated by means of reversed phase high pressure liquid chromatography. In this system, hydralazine inhibited the production of TXB2 (the stable metabolite of TXA2) and enhanced the production of PGF2 alpha and PGE2 in a dose dependent fashion. Indomethacin, blocked the production of all prostaglandin compounds normally synthesized by platelets. These results suggest that hydralazine is a specific thromboxane synthetase inhibitor and that its vasodilatory effects might be related to its ability to block the production of an endogenous vasoconstrictor (i.e. TXA2).