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Biomedical subjects

J R Kahn

Publications and source records attributed to J R Kahn.

At least 19 recordsLinked to original sources
PubMed1999

The gender gap in the economic well-being of nonresident fathers and custodial mothers.

Using a unique sample of couples with children, we estimate the gender gap in economic well-being after marital separation, something that previous studies of individuals who divorce have not been able to do. The income-to-needs levels of formerly married mothers are only 56% those of their former husbands. The postseparation gender gap is reduced if the wife was employed full-time and was an above-average earner before marital disruption. The gap is also relatively small among the least economically independent wives, those who were not employed before separation. For the latter group, the husband's relatively low income tends to reduce the gender gap.

Adult↗
PubMed1992

Intergenerational patterns of teenage fertility.

One of the frequently cited consequences of teen childbearing is the repetition of early births across generations, which thereby perpetuates a cycle of poverty and disadvantage. We use data from the 1988 National Survey of Family Growth (NSFG), Cycle IV, to examine trends and determinants of the intergenerational teen fertility link for women who reached adolescence between the 1950s and the 1980s. We find that daughters of both white and black teen mothers face significantly higher risks of teen childbearing than daughters of older mothers. We also find, more generally, that patterns of teenage family formation (i.e., both marriage and childbearing behaviors) tend to be repeated intergenerationally. The results suggest that the intrafamily propensity for early childbearing is not inherited biologically, at least not through factors related to the timing of puberty. Rather, the intergenerational patterns appear to operate at least in part through the socioeconomic and family context in which children grow up.

Adolescent↗
PubMed1990

Adolescent contraceptive method choices.

This article analyzes determinants of contraceptive method choices among adolescent women in the United States. By using data from the 1982 National Survey of Family Growth, we examined factors that differentiate users of various methods early in the sexual careers of teenaged women. We find that patterns of method choice not only vary by race and region within the United States but also change over the teenager's life course. In addition, among teenagers who did not use a method at first sex, the likelihood of adopting a method soon thereafter was low for both whites and blacks and was unaffected by social structural characteristics.

Adolescent↗
PubMed1989

Sociodemographic determinants of contraceptive method choice in Sri Lanka: 1975-82.

The determinants of contraceptive method choice in Sri Lanka are examined during a period in which contraceptive prevalence increased by over 60% and involved substantial use of sterilization and traditional methods. Data are from the 1975 World Fertility and 1982 Contraceptive Prevalence Surveys. Polytomous logistic regression is used to model four current contraceptive choices: non-use, use of a traditional method, use of a modern temporary method and use of sterilization. The analysis shows, in 1975 and 1982, strong socioeconomic as well as demographic effects on whether any method is used. However, in both years the type of method chosen is primarily a function of demographic considerations related to the couple's family-building stage rather than social status, implying that in Sri Lanka there are few socioeconomic barriers limiting access to different contraceptive methods. The family planning programme, however, has emphasized sterilization rather than birth spacing methods.

Age Factors↗
PubMed1988

City size, quality of life, and the urbanization deflator of the GNP: 1910-1984.

The authors attempt to determine the net effect of city size on quality of life by developing a welfare measure of urbanization. "The estimation procedure suggested in the theoretical part of the paper (section II) is implemented in the empirical part (section III) using 1980 census data from the [U.S.] PUMS (Public Use Micro Data Sample). The results indicate there is no single optimal city size, but rather a worst city size, and about 90 percent of the U.S. population reside in cities smaller than worst city size. If quality of life is related to the degree of urbanization, then long-term trends in the locational distribution of the population should be accounted for in any welfare-oriented measure of national income. One application of our results is, as indicated, the derivation of a GNP welfare deflator reflecting changes in the degree of urbanization (section IV). The findings suggest an urban deflator on the order of six to seven percentage points, which is steadily increasing at a rate of about half a percentage point per decade."

Americas↗
PubMed1988

National estimates of teenage sexual activity: evaluating the comparability of three national surveys.

In this article, we examine the reliability with which teenage sexual activity was reported in three recent national surveys. Unlike other study-effects analyses of objective demographic phenomena such as births and marriages, ours focuses on a more sensitive question--age at first intercourse as reported in three very different surveys. Specifically, we compare reports for the 1959-1963 cohort in the 1979 Kantner-Zelnik Study of Young Women, the 1982 National Survey of Family Growth, and the 1983 wave of the National Longitudinal Survey of Youth. For the ages when the majority of teens become sexually active (16-19), the three surveys provide comparable estimates of early sexual activity. For the younger teen ages, however, there is some disagreement among the estimates. Nevertheless, all three studies produce consistent estimates of the determinants of sexual activity throughout the teen years.

Adolescent↗
PubMed1986

Early subsequent pregnancy among economically disadvantaged teenage mothers.

This study investigated the antecedents and short-term consequences of an early subsequent pregnancy in a sample of economically disadvantaged teenage mothers. Data were gathered over a two-year period from a sample of 675 young mothers living in eight United States cities. Within two years of the initial interview, when half the sample was still pregnant with the index pregnancy, nearly half of the sample experienced a second- or higher-order pregnancy. Characteristics of the young women at entry into the study were relatively poor predictors of which teenagers would conceive again by the final interview. An early repeat pregnancy was associated with a number of negative short-term consequences in the areas of education, employment, and welfare dependency, even after background characteristics were statistically controlled.

Abortion, Induced↗
PubMed1985

Communication and contraceptive practices in adolescent couples.

This study presents a descriptive analysis of the content, frequency, and timing of couple communication regarding birth control among stable, sexually active adolescent couples, and the effect of communication on actual contraceptive practices. The sample consisted of 83 couples in which the female partner was 15-18 years old. All couples had been sexually active at least two months prior to the interview. The majority of couples had discussed birth control on at least one occasion, but discussions prior to first intercourse were atypical. Couples with good communication patterns were more likely to practice effective contraception. One-fourth of the respondents felt that contraception had not been adequately discussed, and these individuals were found to be most at risk to an unintended pregnancy.

Adolescent↗
PubMed1978

A comparison of the substrate specificities of cathepsin D and pseudorenin.

Cathepsin D, purified from hog spleen, releases angiotensin I from tetradecapeptide renin substrate and from protein renin substrates purified from hog and human plasma. However, the enzyme does not act on the naturally occurring renin substrate as it exists in plasma nor on purified substrate in the presence of plasma. Cathepsin D releases angiotensin I quantitatively from tetradecapeptide renin substrate and does not further degrade the angiotensin I on prolonged incubation. The pH optimum for cathepsin D prolonged incubation. The pH optimum for cathepsin D acting on tetradecapeptide renin substrate is 4.5, and there is very low activity above pH 7. These properties are very similar to those of pseudorenin, an angiotensin-forming enzyme originally isolated from human kidney, indicating that cathepsin D and pseudorenin may be identical.

Animals↗
PubMed1978

Multiple forms of renin substrate in human plasma.

Renin substrate (angiotensinogen) in unfractionated human plasma has been shown to exist in multiple forms by DEAE-cellulose chromatography and isoelectric focusing. Two major and 5 to 6 minor peaks were resolved by using a descending pH gradient elution from DEAE-cellulose columns. The two predominant forms were eluted at or near pH 4.8 and 4.4 and usually accounted for 40--50% of the recovered substrate activity. The elution pH values of the various forms were nearly constant among plasmas from normal males and females and in diabetes, early and late pregnancy and estrogen substitution therapy. The relative distribution of components was not affected by prior freezing of the plasma or by dialysis against the column buffer. Eight renin substrate forms were clearly resolved during isoelectric focusing of plasma from a woman on estrogen substitution therapy. Four of these focused at pH 4.79, 4.88, 4.94 and 5.02 in 1% (w/v) ampholytes pH 3.5--5 and were nearly equal in substrate amount. Together these 4 forms constituted 66% of the total recovered activity. A similar pattern but with decreased amounts of each form of substrate was obtained with normal plasma.

Angiotensinogen↗
PubMed1977

Chronic one-kidney hypertension in rabbits. III. Renopressin, a new hypertensive substance.

The blood pressure of rabbits with chronic one-kidney hypertension can be lowered to normal by immunization with hog kidney cortex preparations that do not contain renin, thus providing evidence for a new factor essential for the maintenance of an elevated blood pressure. A search for the new factor has led to the discovery of a hypertensive substance which we have named renopressin. Subcutaneous injection of the new substance into normal rabbits produces a delayed, slow increase in blood pressure, and after a few days the development of a moderate hypertension which persists indefinitely. The response of the blood pressure to renopressin is totally unlike that to renin. While the pressor action of renin can be blocked by an angiotensin II antagonist, the hypertension caused by renopressin cannot. Renin can increase the blood pressure of hypertensive rabbits; renopressin has no effect. The blood pressure of hypertensive rabbits and of normal rabbits made hypertensive by injection of renopressin can be lowered to normal by passive immunization with the same antibody preparation. The evidence is consistent with the possibility that renopressin and the agent causing the elevation of blood pressure in hypertensive rabbits are similar or identical.

Angiotensin II↗
PubMed1977

New developments in our knowledge of the chemistry of renin.

Although the role of renin in hypertension continues to be incompletely defined, recent progress in the chemistry of renin has been considerable. Extensive purifications of hog kidney renin and the renin-like mouse submaxillary gland enzyme have been achieved. Various inhibitory peptides based on tetradecapeptide renin substrate have been useful in renin kinetic studies and in renin affinity chromatography. Classification of renin as an acid protease results from its marked inhibition by pepstatin and from the discovery that free carboxyl at the active site is essential for activity in human and hog kidney and mouse submaxillary gland enzymes. The presence of pseudorenin in all tissues has limited the use of model peptides as renin substrates in plasma and crude tissue extracts, since the proteolytic properties of the two enzymes are nearly identical. The existence of renin in multiple, chromatographically separable forms has been known. More recently inactive forms have been found in plasma, amniotic fluid, and hog and rabbit kidneys. Prolonged storage or treatment with acid, trypsin, or pepsin causes activation; in some instances the conversion is from a higher than normal molecular weight. The implications of these findings with respect to the renin-angiotensin system need much further investigation.

Amino Acid Sequence↗
PubMed1976

The biochemistry of the renin-angiotensin system and its role in hypertension.

The renin-angiotensin system has an important role in maintaining elevated blood pressure levels in certain forms of experimental and human hypertension. Renin, an enzyme produced by the juxtaglomerular cells of the kidney, acts on a protein substrate found in the alpha 2-globulin fraction of the plasma to produce a decapeptide, angiotensin I. This decapeptide is not directly pressor, but on passage through the pulmonary circulation is converted to an octapeptide, angiotensin II, a very potent pressor substance which acts by causing constriction of arteriolar smooth muscle. In addition to its direct action which increases blood pressure, angiotensin II acts on the adrenal cortex to cause the release of the sodium-retaining hormone aldosterone. Recent evidence suggests that this action may be mediated by the heptapeptide, angiotensin III. Both renin and its protein substrate exist in multiple forms and renin may also exist as a high molecular-weight "pro-hormone," although the physiologic significance of these forms is not clear. The elucidation of the biochemistry of the renin-angiotensin system has provided us with inhibitors which allow the system to be blocked effectively in vivo. Thus, angiotensin antagonists such as Sar 1, IIe 8-angiotensin II and converting enzyme inhibitors such as BPP 9a (SQ 20881) have proved useful in the study of experimental and human hypertension.

Aldosterone↗