Chronic exposure to ionizing radiation as a tumor promoter in mouse skin.

We have tested chronic exposure to 90Y beta radiation for its action as a complete tumor promoter, a stage I tumor promoter, or a stage II tumor promoter in SENCAR mouse skin. In skin initiated with a single application of 7,12,dimethylbenz[a]anthracene (DMBA, 10 nmol), chronic exposure to beta radiation as a complete promoter (0.5 Gy, twice/week, 13 weeks) produced no tumors and, when added to a complete chemical promoter (TPA), reduced tumor frequency about 30%. A similar result was observed when beta radiation was tested as a stage II promoter. DMBA-initiated mice that received chemical (12-O-tetradecanoylphorbol-13-acetate, TPA) stage I promotion followed by 13 weeks of beta-radiation exposure (0.5 Gy, twice/week) as stage II promotion produced essentially no tumors, and combining the same chronic beta-radiation exposure with chemical (mezerein) stage II promotion reduced tumor frequency about 20% when compared to a similar group that was not irradiated. Chronic beta-radiation exposure was tested two ways as a stage I tumor promoter in initiated skin that was subsequently treated with mezerein as a stage II promoter. Stage I promotion was shown to proceed with the passage of time, indicating this process occurs naturally in the absence of chemical or physical stimulation. Hyperthermia, previously shown to be a potent inhibitor of chemically stimulated stage I promotion, had no effect on the natural process, indicating at least some differences in mechanism between the two processes. The natural process was, in fact, inhibited by chemical tumor promoters, but not by radiation. In addition to the increase resulting from this natural process, tumor frequency was further increased slightly but significantly (12-15%, P less than or equal to 0.05) when chronic radiation exposure was given as a stage I promoter (0.5 Gy, twice/week, 13 weeks) subsequent to initiation, in spite of the expected 20% reduction resulting from this dose. Exposure of initiated animals to radiation (0.5 or 1.0 Gy, twice/week, 2 weeks) in addition to TPA as stage I promotion produced a similar increase in tumor frequency (P less than 0.02). At higher radiation doses, however, tumor frequency was reduced compared to unirradiated controls. In a third test as a stage I promoter, beta radiation (0.5 Gy twice/week, 4 weeks) was given prior to initiation with N-methyl-N'-nitro-N-nitrosoguanidine in animals subsequently promoted by TPA (twice/week, 13 weeks), and again the radiation slightly but significantly (P less than 0.03) increased tumor frequency compared to the unirradiated control group.(ABSTRACT TRUNCATED AT 400 WORDS)     

Identification of haplotypes in promoter of prolactin gene and their effect on egg production and quality traits in layer chicken

Expression of prolactin hormone is a crucial event in regulating egg production in chickens for which promoter plays the vital role in expressing the prolactin gene. The objective of the present study was to identify haplotypes in the prolactin promoter and their effects on egg production and egg quality traits in White Leghorn chicken. Single stranded conformation polymorphism followed by sequencing was conducted to explore polymorphism at 561 bp promoter of prolactin gene. The effect of haplotype combinations on egg production and quality traits were estimated following general linear model technique. The expression of prolactin by different haplogroups was quantified by qPCR. Total 28 haplotypes were found in White Leghorn chicken of which h1 haplotype possessed the highest frequency of 0.46 and h8, h14, h16, h25, h26, and h28 haplotypes had the lowest frequency (0.1%). The egg production up to 52 and 64 weeks of age were found to be significantly (p < 0.05) associated with haplotype combinations where the highest 52-w (52 weeks) egg production was found in animals with h1/h22 combination and the lowest production was observed in the birds with h1/h2 haplogroup. The haplotype combinations had the significant effect (p < 0.05) on Haugh Unit, yolk index and albumen weight at 40 weeks of age; Haugh Unit and albumen weight at 52 weeks of age and Haugh unit, yolk weight and yolk percentage at 64 weeks of age. The prolactin expression in h1/h22 birds was found to be the lowest and in h1/h5 birds to be the highest. The prolactin expression showed significant effect on 52-w egg production and albumin weight at 52 weeks age. In conclusion, it may be stated that the prolactin promoter was highly polymorphic and had the significant association with egg production and quality traits in White Leghorn chicken.     

Increased sensitivity of mouse mammary gland for hormones and tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate in tissues containing the Mtv-2 gene

We have compared the response of mammary explants obtained from GR mice with those derived from GR/Mtv-2- congenic mice towards hormones and tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA). In explants of the mammary glands of virgin GR mice, insulin, prolactin, progesterone and TPA stimulated the rate of (3H)-thymidine incorporation into DNA. A significantly lower response towards prolactin and TPA was observed in mammary explants derived from GR/Mtv-2-mice. The differential sensitivity of mammary tissues from GR and GR/Mtv-2-mouse strains to the actions of prolactin and tumor promoter is directly correlated to their different incidences of spontaneous tumor formation; it is not known if there is a causal relationship.     

Polymorphism in the Prolactin Promoter and Its Association with Growth Traits in Chickens

The pituitary hormone prolactin has a wide variety of functions involving growth, behavioral, and ovarian activities in chickens. The objectives of the present study were to identify polymorphisms in the prolactin promoter and estimate their effects on growth traits in White Leghorn chickens. Among 28 haplotypes found, the h1 haplotype was predominant. Body weight at 16 and 64 weeks and age at sexual maturity were significantly associated with haplotype combinations (P < 0.05). The h1/h1 haplogroup showed the highest body weight at 16 weeks of age, and h1/h7 was the highest at 64 weeks. The lowest age at sexual maturity was found in birds with the h1/h6 haplotype combination, and mRNA expression of prolactin was lowest in h1/h4 birds and highest in h1/h5 birds. The prolactin promoter was highly polymorphic and had significant associations with growth traits in White Leghorn chickens.     

Prolactin as a promoter of initial progression of spontaneous mammary tumors in mice and lack of relationship to age

In a high mammary tumor strain of SHN virgin mice, the percent increase in the number of palpable mammary tumors during 3 weeks after the 1st tumor appearance was significantly retarded by ovariectomy and this retardation was prevented by pituitary grafting associated with the decrease and the increase in the circulating prolactin levels, respectively. A low mammary tumor strain of SLN virgin mice grafted with a single pituitary each at 2 and 5 months of ages developed mammary tumors 4 and 2 months after grafting (6 and 7 months of ages), respectively. However, there was no difference between groups in mammary tumor incidence at any month after mice in each group developed tumors first. Mammary tumor incidences of both groups were significantly higher than that of the untreated control at all ages examined. These findings have demonstrated that prolactin plays a key role in the initial progression of spontaneous mammary tumors of mice besides its prerequisite role in tumor development. They also suggest that there is no intrinsically age-related difference in prolactin effect on mammary tumorigenesis.     

Deterioration of male sexual behavior in rats by the new prolactin-secreting tumor 7315b

The effects of hyperprolactinemia on male copulatory behavior in adult male and female rats were studied. Hyperprolactinemia was induced by the transplantable purely prolactin-secreting tumor 7315b. Male rats were castrated and received testosterone-filled capsules of different sizes which induced normal and subnormal testosterone levels. After sexual training the rats of the experimental groups were inoculated with tumor 7315b. Three weeks after tumor-inoculation high prolactin levels (2000-30000 ng/ml) were found. During this hyperprolactinemia ejaculation latency increased significantly, while the mount frequency and intromission frequency remained unchanged. Only 9 out of 22 rats ejaculated 19 days after inoculation. Moreover, it appeared that the inhibitory effect of the tumor was as strong in the presence of normal (2.33 +/- 0.07 ng/ml) as in the presence of low (0.35 +/- 0.01 ng/ml) testosterone levels. The inhibitory effect of tumor 7315b on copulatory behavior was not influenced by adrenalectomy. In gonadectomized female rats bearing testosterone-filled capsules tumor 7315b induced prolactin levels of about 2000 ng/ml and an almost complete cessation of mounts and intromission patterns 4 weeks after tumor-inoculation. It was concluded that tumor 7315b causes a strong inhibitory effect on male copulatory behavior in male and female rats and that this effect is not influenced by the presence of normal or low testosterone levels or removal of the adrenals, suggesting a direct effect of prolactin on brain functions.     

Temporal effects of estradiol and diethylstilbestrol on pituitary and plasma prolactin levels in ovariectomized Fischer 344 and Holtzman rats: a comparison of radioimmunoassay and Nb2 lymphoma cell bioassay.

An Nb2 lymphoma cell bioassay (Nb2BA) and a radioimmunoassay (RIA) were used to compare plasma and pituitary levels of prolactin in ovariectomized Fischer 344 (F344) and Holtzman rats treated with either diethylstilbestrol (DES) or estradiol for up to 8 weeks. The objectives were to determine whether there were temporal differences in prolactin responses in strains with different genetic predispositions to estrogen-induced pituitary tumor formation and to determine whether the results of the two assay methods were equivalent. All rats were ovariectomized for 7 days and all except controls received subcutaneous Silastic implants of DES or 17 beta-estradiol and were sacrificed at intervals from 2 days to 8 weeks later. Pituitary content and plasma levels of prolactin were determined by Nb2BA and RIA and the ratio of these measurements was calculated. DES induced a significant increase in pituitary prolactin in F344 rats by 2 days of treatment, as measured by RIA. Pituitary content increased to a peak by Day 4, after which a gradual decline occurred until the end of the experiment. Nb2BA measurements were similar to those obtained by RIA, except at 8 weeks, when the content determined by Nb2BA was significantly higher than the content determined by RIA. When estradiol was given to F344 rats a pattern of increase and subsequent decrease in pituitary content similar to that seen with DES was observed and levels measured by Nb2BA and RIA were essentially equivalent. Plasma levels of prolactin in DES-treated F344 rats increased exponentially through the 8 weeks, and the Nb2BA measurements were significantly greater than levels determined by RIA throughout the treatment period. Estradiol treatment produced a pattern of change in plasma levels of prolactin similar to that observed with DES, except that RIA and Nb2BA measurements were not different. Comparable results were obtained in Holtzman rats, except plasma levels were not increased to the same degree as seen in F344 rats. From these results, we conclude that DES, but not estradiol, can selectively increase the secretion of prolactin that is more bioactive than immunoreactive and that this effect of DES is observed in F344 and Holtzman rats, although F344 rats released more prolactin in response to estrogens than did Holtzman females.     

Positive Prolactin Response to Bromocriptine in 2 Patients with Cabergoline-Resistant Prolactinomas

ObjectiveTo describe a positive prolactin response to bromocriptine treatment in 2 patients with cabergolineresistant prolactinomas.MethodsWe report the patients’ clinical presentations, laboratory test results, imaging findings, and clinical courses.ResultsPatient 1 had a 5-mm pituitary microadenoma that was initially diagnosed at age 30 years. After initial diagnosis, she was treated with transvaginal bromocriptine for 9 years and then subsequently went untreated for 2 years. After developing symptoms of amenorrhea, decreased libido, and hyperprolactinemia, oral cabergoline, 0.5 mg twice weekly, was initiated. Her prolactin concentration remained elevated at 80 ng/mL while taking cabergoline. Her prolactin concentration decreased to 13 ng/mL after her regimen was switched to bromocriptine, 5 mg daily. Patient 2 had a 17-mm pituitary macroadenoma that was initially diagnosed at age 15 years. Oral cabergoline was started at 0.5 mg twice weekly and increased to 1 mg 3 times weekly when prolactin levels continued to rise to 340 ng/mL over 18 months. After visual field defects developed, transsphenoidal surgery was performed. One year after surgery, magnetic resonance imaging showed a 6-to 7-mm pituitary adenoma, and there was a gradual rise in serum prolactin. Her serum prolactin concentration continued to rise to 212 ng/mL with increasing tumor size over 3 years. Cabergoline was discontinued and oral bromocriptine was initiated at a dosage of 10 mg daily. After 4.5 months of bromocriptine therapy, her serum prolactin concentration decreased to 133 ng/mL. However, after 2 months, the macroadenoma continued to increase in size and a visual field defect developed, so another transsphenoidal operation was performed.ConclusionsAlthough cabergoline is generally preferred to bromocriptine for the treatment of patients with prolactinomas because of its better tolerance profile and greater effectiveness, in patients with cabergoline-resistant prolactinomas, a bromocriptine trial should be considered a safe, relatively inexpensive, and well-tolerated alternative. (Endocr Pract. 2011;17:e55-e58)