RADIATION FACTS FOR PUBLIC HEALTH OFFICERS

In the medical use of x-rays a few kinds of examinations contribute a large percentage of the gonadal exposure. Dose reduction to a population need not require total reduction nor restriction of the medical use, but study and attention to a few examinations in the pelvic region may satisfy the most skeptical that the use is justified or indicate the need for modification of our present indications for taking x-rays in this area.The potential dangers of ionizing radiation have long been respected and responsible organizations are constantly studying new developments that might add to the dangers and new knowledge that might affect conclusions.     

THE ORIGIN,FERTILITY AND TRANSMISSION OF MONOSOMICS IN GOSSYPIUM

The origin of 51 monosomic plants in Gossypium hirsutum is described, and the great majority are shown to be fertile and transmissible. Both fertility and transmission rate can be increased by outcrossing and selection. Monosomics which have been isolated in a standard hirsutum background can be recognized by distinct morphological characteristics, including modifications of both vegetative and reproductive structures such as smaller or narrower leaves, smaller flowers or flower parts, and smaller, longer, or partially collapsed bolls. Monosomics involving the large chromosomes, i.e., the A genome, are recovered more frequently than are monosomics of the D (small chromosomes) genome. Furthermore, monosomics of certain of the A chromosomes are recovered more frequently than others. Of 20 identified hirsutum monosomics, 7 are chromosome A-2, 7 are A-4, 3 are A-6, and 1 each is A-1, D-17 and D-18.     

Differential effects of prostaglandin E2 on contractions of airway smooth muscle

In an in vitro muscle bath, the active tension generated by strips of canine tracheal smooth muscle responding to cumulative additions of either histamine (10(-8) to 10(-3) M) or acetylcholine (10(-9) to 10(-3) M) was measured in the absence and presence of prostaglandin E2 (PGE2) (10(-6) to 10(-5) M). When contractile responses of equal magnitude were compared, the contractions elicited by acetylcholine were resistant to the inhibitory effects of PGE2, relative to comparable contractions elicited by histamine. To assess the role of adenylate cyclase in determining the different responses to histamine and acetylcholine in the presence of PGE2, we assayed adenylate cyclase activity in membranes prepared from canine tracheal smooth muscle and found that acetylcholine, but not histamine, decreased PGE2-stimulated adenylate cyclase activity by 48 +/- 2% (mean +/- SE; n = 5). However, in other experiments, we found that even large pharmacological increases in tissue adenosine 3',5'-cyclic monophosphate (cAMP) content only partially inhibited muscarinic tone. Also, exogenously applied analogues of cyclic AMP inhibited contractions induced by histamine more effectively than comparable contractions induced by acetylcholine. We concluded that acetylcholine decreased adenylate cyclase activity in membranes prepared from canine tracheal smooth muscle and that this effect may have contributed to, but did not completely account for, the relative resistance of muscarinic contractions to the inhibitory effects of PGE2.     

Short-term action of insulin on Aplysia neurons: Generation of a possible novel modulator of ion channels

In mollusks as in other animals, peptides can act as hormones, growth factors, and neurotransmitters. The presence of insulin in vertebrate brain as well as its actions on nerve cells led us to examine the electrophysiological effects of the mammalian hormone on Aplysia neurons. Application of insulin extracellularly causes hyperpolarization of L14 and L10, identified neurons of the abdominal ganglion. This hyperpolarization is associated with a decreased membrane conductance that reverses at ?35 mV. We also injected inositol phosphate glycan (IPG) into the identified neurons. This complex sugar, which was purified from rat liver and which is a putative second messenger for insulin in nonneural vertebrate cells (Saltiel and Cuatrecasas, 1986; Saltiel, Osterman, and Darnell, 1988), causes hyperpolarization with decreased membrane conductance in L14 and L10 similar to the effects of insulin. Furthermore, exposure of isolated ganglia to insulin results in the generation of IPG with a compensating decrease in its glycosyl-phosphatidylinositol precursor. We suggest that, in addition to its other roles, insulin may function as a neuropeptide transmitter using IPG as a second messenger.     

Rates and outcome of pregnancies achieved in the first 4 years of an in-vitro fertilization program.

Between Feb. 1, 1984, and Dec. 31, 1987, 578 couples were treated in the in-vitro fertilization (IVF) program at University Hospital, London, Ont. The 160 confirmed pregnancies resulted in 86 deliveries and the birth of 108 babies. There were 20 spontaneous abortions, 12 ectopic pregnancies, 11 presumptive pregnancies, 4 neonatal deaths and 1 stillbirth. At the time of writing, 41 pregnancies of 20 weeks'' gestation or more were in progress. Except for a high cesarean section rate the obstetric outcome of pregnancies achieved with IVF does not appear to be different from that expected for a group of infertile couples treated with conventional therapies. The pregnancy rates varied according to the denominator used.     

A premature acrosome reaction is programmed by mouse t haplotypes during sperm differentiation and could play a role in transmission ratio distortion

Mouse t haplotypes are variant forms of chromosome 17 that can be transmitted at non-Mendelian ratios by heterozygous +/t males. The accumulated genetic data indicate that '+-sperm' and 't-sperm' are produced in equal numbers but that most '+-sperm' are rendered dysfunctional, so that 't-sperm' have a relative advantage at fertilization. To date, the basis for this t-induced sperm dysfunction has remained unknown. Here we demonstrate that a high proportion of sperm obtained from certain strains of +/t mice undergo a premature acrosome reaction under in vitro capacitation conditions. The simplest interpretation of these data, in conjunction with previous results, is that developing '+-spermatids' are preprogrammed by 't-spermatids' to undergo this premature reaction. Since acrosome-reacted sperm are unable to participate in the process of fertilization, this defect could account for the extreme distortion of transmission ratio observed from mice heterozygous for a class of complete t haplotypes.