Effects of butylated hydroxytoluene pretreatment on the metabolism and genotoxicity of aflatoxin B1 in primary cultures of adult rat hepatocytes: selective reduction of nucleic acid binding.

To elucidate biochemical mechanisms underlying the anticarcinogenic activity of butylated hydroxytoluene (BHT), studies were undertaken to characterize the influence of BHT pretreatment on the metabolism and genotoxicity of aflatoxin B1 (AFB1) in primary cultures of rat hepatocytes. During a 10-day pretreatment period, adult male rats were fed either a control diet or a diet supplemented with 0.5% BHT. Hepatocytes were subsequently isolated from each animal and cultured in chemically defined medium. Cultures prepared from rats which had been fed BHT metabolized AFB1 more rapidly than did controls. BHT pretreatment also enhanced oxidation of AFB1 to aflatoxin M1 (AFM1), and accelerated the rate of AFM1 conjugation. Covalent binding to DNA and RNA in BHT-pretreated cultures was reduced by 91 and 82%, respectively, while protein binding decreased by only 29%. AFB1 did not stimulate detectable DNA repair synthesis in BHT-pretreated cultures, although stimulation of DNA repair was clearly evident in control cultures. In a separate experiment, consistently higher baseline concentrations of reduced glutathione were observed in BHT-pretreated cells, indicating that BHT pretreatment may enhance formation of detoxified glutathione conjugates of AFB1. These findings suggest that the anticarcinogenic activity of BHT is due in part to preferential enhancement of hepatic detoxification mechanisms, with the result that intracellular concentrations of reactive metabolites are reduced and fewer covalently bound adducts are formed.

Serum and pituitary concentrations of prolactin and growth hormone in mice during a twenty-four hour period.

The objective of this study was to investigate changes in the secretion of prolactin (PRL) and growth hormone (GH) occurring during a 24 h period in the mouse. Adult female mice of the C57BL/St strain and male mice of the C3H/St strain, maintained on a 14 h light and 10 h dark schedule, were used. Serum and pituitary concentrations of PRL and GH were measured by radioimmunoassay in samples collected by decapitation at hourly intervals through 24 h. Serum PRL concentrations in female mice averaged higher during the daylight hours and lower at night. However, the pattern was just the opposite in males: the values were lower during the day time and higher and variable during the night. Pituitary PRL levels dropped significantly after the onset of the dark phase in mice of both sexes. Serum GH concentrations of female mice did not fluctuate significantly with the time of the day, but those of male mice displayed a distinct flux: the levels were low from 0800 h until 1500 h, began to rise in the afternoon, and remained relatively high throughout the night. Pituitary levels of GH did not change with time in mice of either sex. The data suggest the existence of daily rhythms in the secretion of PRL and GH in mice, with marked differences related to sex. In general, the changes were most pronounced for serum PRL in females and for serum GH in males.

A comparison of the effects of CB-154 and lergotrile mesylate on prolactin and growth hormone secretion in mice.

The influence of 2-bromo-alpha-ergocryptine (CB-154) and 2-chloro-6-methyl-ergoline-8beta-acetonitrile methanesulfonate (lergotrile mesylate) on prolactin (PRL) and growth hormone (GH) secretion in mice was investigated. Both drugs inhibited the nursing-induced rise in serum PRL in lactating mice, CB-154 being effective at a somewhat lower dosage than lergotrile mesylate. Both drugs reduced basal concentrations of serum PRL by more than 90% within an hr after administration, but the effect of CB-154 lasted for several hr longer than that of lergotrile mesylate. CB-154 did not change the resting concentrations of GH in mice, but it promoted the induction of GH release by nursing; injection of lergotrile mesylate, on the other hand, seemed to enhance the basal concentrations of GH in lactating mice that were separated from their young for 12 hr. The results show that both drugs can be used successfully for reducing PRL secretion in the mouse.

Control of prolactin and growth hormone secretion in mice by obesity.

Prolactin (PRL) and growth hormone (GH) secretions in mice rendered obese by the administration of gold thioglucose (GTG) are abnormal. The objective of the present experiments was to determine whether the effects were related to the drug or to the resultant obesity. Perphenazine-induced PRL release in normal mice and in GTG-injected non-obese mice was compared to that of GTG-injected obese mice after the initial development of obesity, after body weight reduction by diet control and after the resumption of obesity by ad lib. feeding. The GTG-injected mice which did not become obese had greater (50%) than normal levels of serum PRL following perphenazine stimulation in 2 of 3 experiments. This suggested that the injection of GTG directly affected the control mechanism for PRL secretion, but that the abnormal PRL secretion was probably not the cause of obesity that develops after GTG treatment. Perphenazine-induced PRL levels in mice rendered obese with GTG were much greater (2-3 times higher than normal). However, the unusually high levels of PRL were totally abolished when the body weights of these mice were brought down to normal by dietary restriction. Conversely, when obesity was permitted to recur by giving the mice free access to food, PRL levels reverted back to the original obese pattern. The concentrations of GH were usually lower than normal in GTG-obese mice, and these levels were also more often associated with the development of obesity than with the injection of GTG. The data show a marked influence of obesity on the control of PRL and GH secretions in the mouse.

Circulating levels of prolactin and growth hormone and natural incidence of mammary tumors in mice.

Radioimmunoassay measurements of hormones in sera show that contrary to expectations, natural mammary tumorigenesis in mice is not always accompanied by high prolactinemia. Basal levels of circulating PRL follow no consistent pattern in relation to the incidence of mammary tumors. Circulating PRL after a provocative stimulus, however, presents a profile characteristic of the mammary tumor incidence: strains with high incidence of mammary tumors generally have have lower levels, whereas strains with low incidences exhibit higher levels. These differences in circulating PRL levels are apparently not caused by differences in the pituitary stores or pituitary release of PRL. The PRL release patterns appear not to be entirely genetic, since they can be modified by foster nursing, a procedure that may introduce MTV in a virus-free strain. The urine concentrations of PRL and GH and the tissue uptake data suggest that the C3H/St strain may metabolize PRL and GH differently from the C5BL/St strain. It remains to be determined whether the observed differences are significant factors in the development of spontaneous mammary tumors in mice.

Prolactin and growth hormone secretion in chemically induced and genetically obese mice.

Experiments were performed to determine PRL and GH concentrations in mice rendered obese by chemical means and to compare these concentrations with those of mice obese as a result of genetic mutation. Basal levels of serum PRL and GH were generally lower in gold thioglucose (GTG) and bipiperidyl mustard (BPM)-treated obese mice compared with lean controls. In the pituitary gland, the hormonal changes varied from lower or unchanged levels of PRL and GH shortly after drug injection to very high concentrations of PRL (but not of GH) a year later. However, when the mice were challenged with perphenazine, a drug that causes prompt release of PRL, GTG and BPM-obese mice released 2-5 times as much PRL as did lean controls, suggesting an impairment in the hypothalamic control of PRL secretion in GTG/BPM-obese mice. Basal levels of PRL and GH in genetically obese (ob/ob) mice of both sexes were also lower than those in their lean relatives (?/+). This was true for both serum and pituitary concentrations of the two hormones, the only exception being pituitary GH concentrations in females which were higher than or equal to those of controls. However, unlike GTG and BPM-obese mice, genetically obese mice released very little PRL compared with their lean relatives when stimulated with perphenazine, which suggested an insufficiency of pituitary function in ob/ob mice. The results demonstrate abnormalities in the secretion of PRL and GH in obese mice of both types.

Prolactin and growth hormone levels in different inbred strains of mice: patterns in association with estrous cycle, time of day, and perphenazine stimulation.

These experiments were designed to compare prolactin (PRL) and growth hormone (GH) secretion in strains of mice with varying incidences of mammary tumors. In addition to the basal levels, PRL concentrations were compared after stimulation with perphenazine. Although pituitary concentrations of PRL and pituitary serum concentrations of GH appeared to be generally higher in strains with high incidence of mammary tumors, basal PRL levels in single decapitate serum samples seemed to have little correlation with the incidence of mammary tumors in different strains. However, PRL concentrations in sera after perphenazine injection followed a pattern characteristic of the mammary tumor incidence rate of the strain: C3H/St and CBA/St--the two high-incidence strains--had lower levels of PRL; C57BL/St and BALB/cST--the two low-incidence strains--had higher levels; and DBA/2St--the medium-incidence strain--had an intermediate level. PRL contents of the pituitary glands were depleted virtually equally in all strains except the BALB/cSt. These results suggested that the rate of metabolism of PRL in strains with high incidence of mammary tumors may be faster than in those with low incidences. Perphenazine had no influence on GH secretion in most mice. The strain-specific differences in PRL and GH concentrations were usually present even during cyclical and diurnal fluctuations. Serum PRL and GH levels were generally higher during the follicular phase and lower during the luteal phase of the estrous cycle in both C3H/St and C57BL/St strains. There were signs of episodic secretion of PRL together with evidences of circadian periodicity in the secretion of PRL and GH in mice of both strains. The levels of GH were usually high during the morning hours of those of PRL high during the evening hours. The data show a high degree of specificity in the secretion of PRL and GH im mice of different inbred strains, and it is possible that these strain-specific differences may be an important factor in the development of mammary tumors.

Pituitary and serum concentrations of prolactin and GH in Snell dwarf mice.

Secretions of prolactin and GH in dwarf mice were studied using homologous radioimmunoassays. Blood samples from adult male and femal dw/dw mice were collected by orbital puncture and by decapitation. Compared to related normals (+/?), pituitary concentrations of GH and prolactin were very low in dw/dw mice, the concentrations of prolactin being more scarce than those of GH. Prolactin and GH concentrations were also lower in sera of dw/dw mice, but the relative differences appeared sex-dependent: serum GH was more reduced in males than in females while serum prolactin was more depressed in females. The data confirm earlier indications of deficiencies in the circulating levels of prolactin and GH in dwarf mice and suggest that the hypoactivity of these hormones may be crucial to some of the anomalies found in this mutant.