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Hormonal Basis (hormonal + basis)

Distribution by Scientific Domains
Life Sciences50%

Selected Abstracts

The Structural and Hormonal Basis of Sex Differences in Peak Appendicular Bone Strength in Rats,,

JOURNAL OF BONE AND MINERAL RESEARCH, Issue 1 2003
Bom-Taeck Kim
Abstract To identify the structural and hormonal basis for the lower incidence of fractures in males than females, sex differences in femoral mid-shaft geometry and breaking strength were studied in growth hormone (GH)-replete and -deficient male and female rats. Sexual dimorphism appeared during growth. Cortical thickening occurred almost entirely by acquisition of bone on the outer (periosteal) surface in males and mainly on the inner (endocortical) surface in females. By 8 months of age, males had 22% greater bone width and 33% greater breaking strength than females. Gonadectomy (Gx) at 6 weeks reduced sex differences in bone width to 7% and strength to 21% by halving periosteal bone formation in males and doubling it in females. Gx had no net effect on the endocortical surface in males but abolished endocortical bone acquisition in females. GH deficiency halved periosteal bone formation and had no net effect on the endocortical surface in males, but abolished bone acquisition on both surfaces in females, leaving males with 17% greater bone width and 44% greater breaking strength than females. Sex hormone deficiency produces greater bone fragility in males than females by removing a stimulator of periosteal growth in males and removing an inhibitor of periosteal growth in females. GH deficiency produces less bone fragility in males than females because males retain androgen-dependent periosteal bone formation while bone acquisition on both surfaces is abolished in females. Thus, periosteal growth is independently and additively stimulated by androgens and GH in males, inhibited by estrogen, and stimulated by GH in females. The hormonal regulation of bone surfaces establishes the amount and spatial distribution of bone and so the sexual dimorphism in its strength. [source]

Experimental determination of the periodicity of incremental features in enamel

JOURNAL OF ANATOMY, Issue 1 2006
T. M. Smith
Abstract Vital labelling of hard tissues was used to examine the periodicity of features of dental enamel microstructure. Fluorescent labels were administered pre- and postnatally to developing macaques (Macaca nemestrina), which were identified histologically in dentine and related to accentuated lines in enamel, allowing for counts of features within known-period intervals. This study demonstrates that cross-striations represent a daily rhythm in enamel secretion, and suggests that intradian lines are the result of a similar 12-h rhythm. Retzius lines were found to have a regular periodicity within individual dentitions, and laminations appear to represent a daily rhythm that also shows 12-h subdivisions. The inclusion of intradian lines and laminations represents the first empirical evidence for their periodicities in primates; these features frequently complicate precise measurements of secretion rate and Retzius line periodicity, which are necessary for determination of crown formation time. The biological basis of incremental feature formation is not completely understood; long-period features may result from interactions between short-period rhythms, although this does not explain the known range of Retzius line periodicities within humans or among primates. Studies of the genetic, neurological and hormonal basis of incremental feature formation are needed to provide more insight into their physiological and structural basis. [source]

The Structural and Hormonal Basis of Sex Differences in Peak Appendicular Bone Strength in Rats,,

JOURNAL OF BONE AND MINERAL RESEARCH, Issue 1 2003
Bom-Taeck Kim
Abstract To identify the structural and hormonal basis for the lower incidence of fractures in males than females, sex differences in femoral mid-shaft geometry and breaking strength were studied in growth hormone (GH)-replete and -deficient male and female rats. Sexual dimorphism appeared during growth. Cortical thickening occurred almost entirely by acquisition of bone on the outer (periosteal) surface in males and mainly on the inner (endocortical) surface in females. By 8 months of age, males had 22% greater bone width and 33% greater breaking strength than females. Gonadectomy (Gx) at 6 weeks reduced sex differences in bone width to 7% and strength to 21% by halving periosteal bone formation in males and doubling it in females. Gx had no net effect on the endocortical surface in males but abolished endocortical bone acquisition in females. GH deficiency halved periosteal bone formation and had no net effect on the endocortical surface in males, but abolished bone acquisition on both surfaces in females, leaving males with 17% greater bone width and 44% greater breaking strength than females. Sex hormone deficiency produces greater bone fragility in males than females by removing a stimulator of periosteal growth in males and removing an inhibitor of periosteal growth in females. GH deficiency produces less bone fragility in males than females because males retain androgen-dependent periosteal bone formation while bone acquisition on both surfaces is abolished in females. Thus, periosteal growth is independently and additively stimulated by androgens and GH in males, inhibited by estrogen, and stimulated by GH in females. The hormonal regulation of bone surfaces establishes the amount and spatial distribution of bone and so the sexual dimorphism in its strength. [source]

Genital swellings in silvered langurs: what do they indicate?

AMERICAN JOURNAL OF PRIMATOLOGY, Issue 5 2007
Nichole Shelmidine
Abstract The occurrence of genital swellings was examined in adult female silvered langurs (Trachypithecus cristatus). In contrast to the exaggerated swellings found in cercopithecines and apes, genital swellings in silvered langurs are confined to the vulva and the surrounding perineum, but they may nevertheless convey information similar to that of exaggerated swellings (i.e., correlate with the receptive period and fertility). If so, genital swellings would be expected to occur most frequently in cycling females, and sexual behavior and male interest should most frequently involve females with swellings. Swellings during gestation, if they occur at all, should be most pronounced at the beginning. Swelling sizes (in three size categories) in nine adult females were examined throughout different reproductive states (cycling, pregnant, and lactating), and in relation to proceptivity, receptivity, and attractivity. Data were collected from November 2002 through March 2004 (on 500 of the 502 calendar days) at the Wildlife Conservation Society's Bronx Zoo. Female sexual behavior (proceptivity and receptivity) and male inspection (attractivity) were recorded each day for 6,hr by video camera (2,948,hr total) and analyzed as present or absent for each female day. Swellings were assessed directly (not from videotapes). In contrast to the predictions, swellings occurred significantly less frequently in cycling females (compared to pregnant females) and no regular, cyclic pattern could be detected. Some females conceived without a swelling. Female attractivity was independent of swellings but coincided with proceptive behavior. Swellings occurred most frequently in pregnant females, especially toward the end of the gestation period. Therefore, genital swellings in silvered langurs are not similar to exaggerated swellings or the smaller genital swellings that have been described for some other primates. It is currently not clear what they signal to conspecifics. Male behavior needs to be studied in more detail, and the hormonal basis for these swellings should be explored. Am. J. Primatol. 69:519,532, 2007. © 2006 Wiley-Liss, Inc. [source]