Presence but not synthesis of thyrotrophin-releasing hormone in rat salivary glands detected by radioimmunoassay and northern blot analysis.

Thyrotrophin-releasing hormone (TRH) is one of the ubiquitous peptides first isolated from hypothalamus. This study sought to examine if it could also be detected in rat submandibular salivary glands, as can other neurogastrointestinal peptides. Radioimmunoassay of submandibular gland homogenates revealed TRH-like immunoreactivity in all samples from male rats (637.34 pg/gland +/- 166.17, n = 15). In contrast, Northern blot analysis to determine whether the peptide was locally synthesized in the glands failed to detect TRH mRNA. Consequently, the presence of TRH in the glands (as revealed by radioimmunoassay) could be associated with binding to presumptive TRH receptors in the mediation of physiological activities.

[Scanning electron microscope view of dentin exposed to CO2 laser radiation]. / Aspect en microscopie electronique a balayage de la dentine exposée à un rayonnement laser CO2.

In order to better define the effects of CO2 Laser rays on dentine, 10 healthy human teeth to be removed and 64 recently removed healthy human teeth were prepared and irradiated according to the classic protocol used in clinical periodontics, and observed with a scanning electron microscope. The examination of these samples confirms the phenomena of dentin fusion and recrystallization. But these alterations result in the appearance of a reorganized superficial layer consisting of unevenly juxtaposed craters formed by the pin-point action of the laser beam. These craters present numerous fissures and openings of variable diameter. They do not form a homogeneous surface, since chips may be raised, demonstrating the fragility of the reorganized layer and a lack of cohesion of the underlying dentine. The modified dentine layer also disappears when a curette is used, revealing a very uneven surface crossed with small cracks and where the tubule openings become visible. Our results, unlike many more optimistic studies, still prompt us to exert caution in the systematic use of CO2 lasers in Periodontics.